Jean-Luc Putaux
email: jean-luc.putaux@cermav.cnrs.fr

Nicole Montesanti

Gabrielle Véronèse

Alain Buléon

Morphology and structure of A-amylose single crystals

Keywords: A-amylose, single crystals, electron diffraction, polar crystal, synthetic amylose

A-type single crystals were prepared in dilute water/acetone solutions by crystallizing narrow fractions of short amylose chains biosynthesized in vitro. The 5 µm-long spindle-shaped crystals were observed by scanning and transmission electron microscopy. Electron diffraction patterns were recorded from frozen-hydrated crystals at different tilt angles around selected crystallographic axes. In particular, a series of patterns corresponding to [hk0] zone axes was collected by rotation around the long dimension of the crystal. A description of the crystal habit was proposed by correlating the electron diffraction data with the microscopy images. The double helices are oriented along the long dimension of the crystal (c-axis) and packed in a parallel fashion into lamellae with a parallelogram cross-section defined by the a and b axes of the monoclinic unit cell. A-amylose single crystals are polar objects that grow in the direction of the reducing end of the amylose chains, and the c-axis is oriented opposite to the growth direction.

Introduction

Amylose, the linear constituent of starch, consisting of a(1,4)-linked D-glucopyranosyl units, can be recrystallized in vitro into the so-called A and B allomorphs that also occur in the native granules. Typically, A-type starch is found in cereals while B-starch frequently occurs in tubers and amylose-rich starches [1]. The determination of the distribution and size of crystalline domains in starch granules is difficult due to their complex multilayered ultrastructure and low crystallinity. Crystals grown in vitro have thus been used to collect high resolution diffraction data and propose molecular models that were transposed to the crystalline domains of native starch granules.

A three-dimensional model of the A allomorph was first proposed by Wu and Sarko using fiber X-ray diffraction data collected from stretched films of long-chain amylose. In this model, amylose was crystallized as parallel-stranded right-handed 6-fold double helices organized in an antiparallel fashion in an orthorhombic unit cell [2]. A-type single crystals were prepared by Buléon et al. by addition of ethanol to a hot dilute aqueous solution of short amylose chains stemming from acid hydrolysis of potato starch with an average degree of polymerization 𝐷𝑃 #### of 15 [3]. For the first time, electron diffraction patterns were recorded from frozen-hydrated crystals but the collected data did not allow to confirm the symmetry and unit cell proposed by Wu and Sarko. Spindle-shaped crystals were also prepared by Imberty et al. from potato starch dextrins by diffusion of acetone vapors at 60 °C [4,5]. The general crystal morphology was described from transmission electron microscopy (TEM) images and from electron diffraction patterns of frozen-hydrated specimens, the authors deduced the axial orientation of the c-axis of the unit cell. After analysis of a set of electron diffraction patterns recorded at different crystal tilts, and reindexing of Wu and Sarko's X-ray diffraction patterns, an improved structure was proposed, combining conformational analysis and X-ray refinement. The revised model was based on a monoclinic unit cell containing parallel 6-fold left-handed double helices and 4 water molecules per unit cell [5]. More recently, Popov et al. confirmed the monoclinic nature of the unit cell using synchrotron X-ray microdiffraction data recorded from single crystals prepared from amylose biosynthesized in vitro [6]. The structure was refined using high resolution diffraction data sets collected from several single crystals and the resulting model allowed to describe new fine details of A-amylose [7]. In particular, the double helices were distorted in order to accommodate intra-crystalline pockets of water molecules located between the helices. The total amount of water in the crystal was found to be twice that proposed by Imberty et al. [5].

In a previous work, we have studied the influence of chain length, polydispersity and branching degree of short-chain amylose on the morphology of A-type crystals prepared from dilute aqueous solutions, at 60 °C, in the presence of acetone [8]. In particular, rosettes or fan-like assemblies of 5-10 µm-long spindle-shaped crystals were obtained from narrow fractions of amylose synthesized in vitro from sucrose by the recombinant amylosucrase from Neisseria polysaccharea. The morphological analysis of the single crystals combined with preliminary electron diffraction data showed that the growth direction coincided with but was opposite to the c-axis of the monoclinic unit cell. The axial growth of A-amylose thus clearly appeared to be favored unlike in the case of most polymer single crystals [8].

In the present complementary paper, we provide the first detailed description of the habit of faceted A-amylose single crystals based on an extensive electron diffraction analysis carried out in relation with the crystal morphology determined from scanning and transmission electron microscopy images. We have indexed the growing faces and determined the polarity of the amylose chains with respect to the growth direction.

Experimental section

Preparation of the synthetic amylose fractions

Linear a(1,4)-D-glucan chains were synthesized in vitro by the purified recombinant amylosucrase from Neisseria polysaccharea, as described elsewhere [8]. The synthesis reaction was performed at 30 °C during 24 h in a 50 mM Tris-HCl buffer at pH 7.0, from 600 mM sucrose as glucosyl donor and 100 mM maltose as acceptor, using 0.5 U/mL glutathione-Stransferase/amylosucrase. The resulting products (fructose and maltooligosaccharides of DP ranging from 2 to 36) were subsequently fractionated by preparative gel filtration using a 480 mL column of Biogel P6 Extra Fine (Biorad). Sugars were eluted at 60 °C in water using a flow-rate of 0.66 mL/min. High-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) was used to determine the DP distribution of each resulting fraction of short amylose chains. In the following, these fractions are referred to as SAA (for "synthetic amylose amylosucrase"), associated to their minimum and maximum DP, respectively. As described in details in Supplementary Material, the fractions are characterized by their number-and weight-average mean DPs (𝐷𝑃 $ ##### and 𝐷𝑃 % ###### , respectively) and polydispersity

index P = 𝐷𝑃 % ###### /𝐷𝑃 $ ##### [8]
. Since for the electron crystallography study, it was necessary to select crystals with a clearly faceted shape and a thickness not exceeding 200 µm, only two fractions have been considered: SAA12-23 (𝐷𝑃 $ ##### = 16.4, 𝐷𝑃 % ###### = 16.7, P = 1.013) and SAA17-28 (𝐷𝑃 $ ##### = 20.9, 𝐷𝑃 % ###### = 21.0, P = 1.006).

Crystallization

The protocol was adapted from the procedures described by Buléon et al. [3] and Imberty et al. [5]. Aqueous dispersions of amylose (0.05% w/v) were submitted to nitrogen bubbling for 20 min and heated in sealed vials at 150 °C for 15 min. The solutions were then cooled down DP n to 80 °C, filtered through 0.2 µm pre-heated Sartorius Minisart RC 25 filters, heated again at 150 °C for 15 min, cooled down to 80 °C and poured in a three-neck 100 mL glass balloon preheated at 55 °C in an oil bath. Acetone was heated at 60 °C in a separate compartment and the resulting vapors diffused through pre-heated glass tubes into the amylose solution under gentle stirring. Upon crystallization, the mixtures were allowed to slowly cool down to room temperature. All specimens were kept in their water-acetone mother liquor and stored at 4 °C.

Scanning electron microscopy (SEM)

Drops of dilute crystal suspensions were allowed to dry onto copper stubs. The specimens were coated with Au/Pd and observed in secondary electron mode with a JEOL JSM-6100 scanning electron microscope operating at 8 kV. A second group of specimens were coated with a 2 nm-thick layer of Pt/Pd and secondary electron images were recorded with a JEOL JSM-7000F microscope equipped with a field emission gun and operating at 1.5 kV.

Transmission electron microscopy (TEM) and electron diffraction

Drops of dilute crystal suspensions were deposited onto glow-discharged carbon-coated copper grids and the liquid in excess was blotted with filter paper. The specimens were rapidly mounted on a Gatan 626 specimen holder, quench-frozen in liquid nitrogen, transferred into the microscope and cooled down to -180 °C. The crystals were observed at low temperature, in low illumination conditions, using a Philips CM200 'Cryo' microscope operating at 80 kV for imaging and 200 kV for diffraction. Electron diffraction diagrams were recorded on 1 µm 2 circular areas of single crystals that were tilted around selected reciprocal axes. For calibration purpose, crystals were deposited onto gold-coated TEM carbon films and the diffraction spots were calibrated at low temperature using the diffraction rings of gold. The images were recorded on Kodak SO163 films and the diffraction patterns on Fujifilm imaging plates, read with a Fujifilm BAS-1800II bioimaging analyzer. After indexation and calibration of the diffraction spots, the unit cell parameters were calculated using a least-squares program.

Results

SEM images of the crystals prepared from fractions SAA12-23 and SAA17-28 are shown in Figures 1a,b and1c,d, respectively. In both cases, the crystals are 5 µm-long, 200 nm-thick and about 1 µm-wide spindle-shaped platelets with a flat apical end. In addition, FEG-SEM images show the layered structure of the crystals and the constituting lamellae lie perpendicular to the growth axis (Figure 2a). For both samples, the characteristic shape of the crystal cross-section is a parallelogram (Figures 1b and1d) whose orientation is always the same with respect to the crystal long axis (Figure 2b). The obtuse angle between the faces is about 120°. As this value is close to that of the angle between the a and b axes of the monoclinic unit cell (about 122°), two hypotheses can be made: i) the parallelogram section is a projection of the (a,b) base plane (Figure 2c); ii) the widest face contains the a-axis (the aparameter of the unit cell being larger than the b-parameter) [5]. These assumptions led us to orient the three a, b and c axes as described in Figure 2b. The c-axis would thus point in a direction opposite to the growth direction of the crystal.

Diffraction diagrams were recorded from single crystals lying flat on the carbon film without tilting the specimen holder (Figure 3a). Two equiprobable patterns were observed that were compared to those reported by Imberty et al. Crystals with their long axis oriented parallel to the tilt axis of the specimen holder were selected for tilt experiments. Two approaches were used to record diffraction patterns. On the one hand, thanks to the high sensitivity of the imaging plates, the electron dose could be reduced in such a way that up to five diffraction patterns could be consecutively recorded from the same crystal at different tilt angles. In general, the last two patterns did not extend to a high resolution due to the accumulated radiation damage but the remaining spots were sufficient to identify the corresponding zone axis. On the other hand, we directly tilted the crystals at specific angles (within a ±35° range) and recorded unique high-resolution patterns with a higher electron dose. These experiments allowed us to collect the main patterns corresponding to low-index zone axes and establish their order of appearance as a function of the positive or negative angle around the tilt axis.

Two series of diffraction patterns sequentially recorded at selected tilts around the crystal long axis are shown in Figure S1. The characteristic shape of the crystals, with distinct sharp and flat ends, was used to select crystals oriented parallel to the tilt axis of the specimen holder but pointing in two opposite directions. The initial patterns, recorded with an untilted specimen holder (i.e., 0°), correspond to the [140] zone axis. The [130] and [120] zone axes were reached with relative tilt angles of ±10° and ±30°, respectively, but the series were recorded by tilting the specimen anticlockwise in one case and clockwise in the other (Figure S1a and S1b, respectively). By using the scheme in Figure 4, the c-axis could thus be unambiguously oriented as pointing opposite to the growth direction.

In all patterns, the two main axes were perpendicular, meaning that the a and b angles of the unit cell were 90° and that a triclinic structure could thus be discarded. In addition, Imberty et al. had shown that the patterns recorded at opposite tilt angles around the c-axis with respect to the [010] zone axis were different, allowing to discard an orthorhombic structure [5]. We could not reproduce this experiment since the large tilt angles that were required could not be reached with our set-up. From these two results, it was deduced that the unit cell was monoclinic.

Figure 5a shows a series of TEM images of one crystal rotated around the c-axis. A slight axial curvature was observed when the tilt angle exceeded ±20°. Since the crystals were frozen-hydrated before their introduction in the microscope, we do not believe that this curvature was induced by dehydration due to drying and it rather might be a morphological feature that will require further investigation. The contrast variation at the edges of the crystal could also be interpreted considering the parallelogram shape of its cross-section (Figure 5b).

By drawing the projection of the reciprocal lattice associated to the crystal at each tilt angle, we have identified the zone axis parallel to the electron beam for each image (Figure 5c). In particular, the contrast of the crystals was uniform and its edges appeared to be sharp when its orientation was such that the [010] axis was parallel to the electron beam.

The combination of the results obtained from Figure 5 and Several diffraction patterns corresponding to zone axes which did not belong to the [hk0] series were also recorded, mostly from crystals prepared from fraction SAA12-23. It is likely that the crystals were supported by a deformed carbon film that was tilted even when the specimen holder was not. As it proved difficult to identify the indices of the zone axes by exploring the reciprocal lattice, we have simulated a series of diffraction diagrams corresponding to low-index zone axes using the atom coordinates given by Popov et al. [7] and the Cerius 2 software [START_REF]Cerius 2 program from[END_REF]. The resulting patterns were compared to the experimental ones.

This revealed that most zone axes belonged to the All indexed diffraction patterns were calibrated using a gold standard. Merging the data resulted in a list of 183 independent reflections (Table S1), extending to a 0.1 nm resolution.

The unit cell parameters were calculated from the whole data set using a least-squares regression and imposing a monoclinic constraint: a = 2.098 nm, b = 1.147 nm and c = 1.062 nm, g = 121.46°. These values agree with those reported by Imberty et al. [5] and Popov et al.

[7], determined from electron or X-ray diffraction data (Table 1). However, they match more closely the cell parameters of Popov et al., determined from X-ray microdiffraction data collected at low temperature (-173 °C).

Discussion

The thorough structural and morphological analyses carried out from electron diffraction data and electron microscopy images allowed us to propose an accurate description of the crystal habit of A-amylose single crystals. The main features are summarized in Figure 7.

Morphology

A-amylose single crystals prepared from short amylose chains, typically with 12 < DP < 30, are thick lamellar platelets [8], the lamellae lying perpendicular to the growth direction. The electron diffraction data confirmed the monoclinic unit cell proposed by Imberty et al. [5] and Popov et al. [7], with the c-axis oriented in a direction parallel but opposite to that of the crystal growth. We have unambiguously identified the facets of the crystal: the widest one is the (010)

face which contains the a-axis. The thinnest face is (100) and contains the b-axis. The flat apical end is the (001) face. The parallelogram cross-section of the crystal thus corresponds to a projection of the (a,b) plane. According to the 3D model proposed by Popov et al. [7], the amylose double helices have a "parallel-down" orientation in the unit cell. The non-reducing end of the chains would thus point toward the c-axis and opposite to the growth direction (Figure 7).

The orientation of the A-amylose unit cell in the crystal differs from that observed in lamellar polymer crystals prepared from dilute solutions, for which the c-axis is perpendicular to the lamella base plane. In particular, this is the case for several polysaccharides such as cellulose [START_REF] Buléon | [END_REF][11][12], chitin [12], or the V form of amylose crystallized in the presence of various complexing agents [1]. Lamellar crystals have also been prepared from numerous synthetic polymers [13].

The axial orientation of the chains in the spindle-shaped A-amylose crystals thus appears to be a rather unique feature. In some aspects, this case has similarities with that of the semicrystalline collagen fibrils prepared in vitro from dilute [14] or concentrated [15] solutions.

These fibrils are formed by axial growth of an assembly of triple helices, organized in a quasihexagonal lattice, and exhibit parabolic ends [16,17]. Although the crystalline nature and the molecular packing structure of collagen fibrils is still debated, it may be interesting to explore this analogy in further details.

The reason of the favored axial growth of A-amylose crystals is still unknown. Several observations and hypotheses were discussed in our previous paper in view of classical polymer growth mechanisms [8]. Further investigations will consist in evaluating the influence of operating parameters such as amylose concentration, nature of the precipitant, crystallization temperature and time on the crystal morphology and growth.

Polarity

Since its constituting helices point in the same direction in the unit cell, an A-amylose single crystal can thus be described as a polar object, having reducing and non-reducing edges that would correspond to the apical and nucleation ends, respectively (Figure 7). Chemical polarity in a solid can be desired to confer specific properties, in particular optical and electronic ones, to materials. Several papers describe the in vitro elaboration of polar crystals from small molecules [18,19]. It appears that the assembling of molecules in an antiparallel fashion is generally favored, which explains why polar solids prepared by recrystallization from dilute solutions are quite rare.

While the polar nature of A-amylose single crystals was deduced from the 3D model that involves the parallel packing of double helices, it is yet to be confirmed experimentally. The nanocrystals [22]. Biotin was then labeled by streptavidin-functionalized gold nanoparticles. All these methods involved incubations at temperature of 50-65 °C. They may be adapted to the case of A-amylose crystals but it would be first necessary to test the stability of the crystals dispersed in an acetone-free aqueous medium, in particular during incubations at 50-60 °C. It may thus be necessary to incubate the crystals at a lower temperature but during longer times.

The labeling methods previously described allowed to unambiguously determine the direction of in vivo biosynthesis of cellulose I and b-chitin and, in both cases, it was shown that the microfibrils were biosynthesized by addition of glucosyl units on the non-reducing end of the individual polysaccharide chains [20,22]. The case of starch is different in the sense that the biosynthesized macromolecules are assembled into a microfibrillar form. In particular, according to the accepted cluster model of amylopectin (the branched glucan and main constituent of starch that is partially crystalline in native granules), one macromolecule only has one reducing end and a very large number of non-reducing ends corresponding the end of the short linear branches [23]. The in vivo biosynthesis of amylopectin is currently described by the coordinated action of three enzyme activities (elongation, branching, debranching) [24].

During the branch elongation, the addition of glucosyl units occurs on the non-reducing end of the linear chains [25]. Considering this divergent synthesis of amylopectin, one can assume that the short branches, that would later associate to form crystalline lamellae (with A-or Btype, depending on the botanical source), would thus have their non-reducing end oriented toward the surface of the growing granule [1]. However, the radial development of starch granules in the direction of the non-reducing end of the chains has not been demonstrated experimentally, mostly because of the difficulty to probe the complex ultrastructure of starch granules at a local scale.

The combination of the electron crystallography analysis of in vitro single crystals and the molecular model proposed by Popov et al. [7] led us to conclude that A-amylose single crystals axially grew in vitro in the direction of the reducing end of the chains whereas amylopectin would be biosynthesized outward in native starch granules, in the direction of the non-reducing end.

The results obtained from A-amylose can be compared to those reported for other polysaccharide crystals grown in vitro from dilute solutions: cellulose II [START_REF] Buléon | [END_REF] and IV [11], inulin [26], chitosan [27], b(1,4)-xylan [28], dextran [29] and mannan I [30]. In all cases, it has been shown that the constituting molecules were organized in an antiparallel fashion. In addition, several works on single helical V-amylose have proposed antiparallel packings of single helices, which resulted from two kinds of observations. On the one hand, chain-folding is involved when the amylose chains are longer than the thickness of the lamellar crystals [31,32].

On the other hand, the space groups deduced from the symmetries of the electron diffraction patterns of the single crystals have generally imposed packings of antiparallel chains [33][34][35][36][37].

The case of A-amylose crystals, made of parallel chains, thus appears to be rather unique among recrystallized polysaccharides. Only B-amylose was also described as a hexagonal packing of 6-fold parallel double helices [38,39]. Lamellar single crystals of B-amylose are extremely difficult to prepare [3] and so far, since it has not been possible to grow single crystals as large as those of A-amylose for X-ray microdiffraction study, a detailed molecular model of B-amylose is yet to be proposed.

Tables and Figures

[ 5 ]

 5 as corresponding to the[130] and[140] zone axes of the monoclinic unit cell (Figures3b and 3c, respectively). We have thus used these patterns as references to rapidly select crystals for further tilt experiments.Using the previous hypotheses on the orientation of the a, b and c axes with respect to the crystals, we have calculated a priori the tilt angles around the c-axis that would allow reaching a number of low-index [hk0] zone axes of the monoclinic unit cell. The corresponding diagram is presented in Figure4. The cross-section of the crystal, defined by the a and b axes in real space, has been superimposed on the associated reciprocal lattice. One can see that when a crystal is lying flat on the carbon film at a 0° tilt angle, the axis perpendicular to its surface is not a low-index zone axis and is located between the [130] and [140] axes. This explains why both diffraction patterns shown in Figure3were equiprobable: depending on slight local tilts of the supporting carbon film (within a ±5° range), the crystal may have been oriented in such a way that the [130] or [140] axis was parallel to the electron beam.

  Figure S1 allowed us to unambiguously assign a zone axis to each [hk0] diffraction pattern and fully index the reflections. Four typical patterns corresponding to the [010], [140], [130] and [110] zone axes are displayed in Figure 6 along with the associated spot indexation and orientation of both reciprocal lattice and crystal cross-section. Additional patterns corresponding to [160], [250] and [120] zone axes are shown in Figure S2.

  [1k1] series recorded by tilting the crystals around the [ 01] axis. The diagrams corresponding to [121], [131], [141] and [161] zone axes are displayed in Figure S3. Two additional patterns, shown in Figure S4, recorded by randomly titling the crystals, could be indexed as corresponding to [021] and [143] zone axes.

  polarity of other polysaccharide crystals has already been investigated by TEM imaging and electron diffraction in the case of native cellulose I and b-chitin microfibrils. All methods were based on the selective labeling of the polysaccharide reducing end, the crystals being made of parallel chains. Koyama et al. have grown electron-dense silver nanoparticles on the reducing end of cellulose I nanocrystals [20]. Another method was described by Kim et al. who labeled the aldehyde groups at the reducing end of cellulose I microfibrils with colloidal gold nanoparticles [21]. More recently, Imai et al. grafted biotin on the reducing end of b-chitin

  (a) monoclinic parameters calculated from the orthorhombic unit cell proposed by Wu and Sarko [2]; (b) Imberty et al. [4]; (c) monoclinic parameters calculated from the orthorhombic unit cell proposed by Imberty et al. [5]; (d) Popov et al. [7]; (e) volume of the monoclinic unit cell: V = a.b.c.sing.

Figure 1 .

 1 Figure 1. SEM images of A-amylose single crystals prepared from fractions SAA12-23 (a,b) and SAA17-28 (c,d). In b and d, the crystals are organized in rosettes and their parallelogram cross section can clearly be seen.

Figure 2 .

 2 Figure 2. a,b) FEG-SEM images of single crystals prepared from fraction SAA12-23. In b, the main axes of the monoclinic unit cell have been superimposed to crystals in different orientations. c) Schematic representation of the amylose double helices in the monoclinic unit cell. The discs (left) and rods (right) correspond to end-on and edge-on views, respectively, of the double helices.

Figure 3 .

 3 Figure 3. a) TEM image of an A-amylose single crystal prepared from fraction SAA17-28; b,c) most frequently observed electron diffraction patterns collected from untilted single crystals lying flat on the carbon film, correctly oriented with respect to the crystal in image (a). According to the indexation proposed by Imberty et al. [5], the zone axes are [130] (b) and [140] (c), respectively.

Figure 4 .

 4 Figure 4. Projection of the reciprocal lattice (black dots) of the monoclinic unit cell of A-amylose along the c/c*-axis. The crystal cross-section in real space (in grey) was superimposed to the reciprocal lattice. The a and b axes are indicated by the dotted lines. The dense planes of the reciprocal lattice are indicated by continuous lines. The Miller indices correspond to the axis perpendicular to the selected lattice planes. The tilt angles allowing to bring the zone axis parallel to the incident electron beam are indicated in parentheses.

Figure 5 .Figure 4 .

 54 Figure 5. Relationship between the variation of contrast in the TEM images of an A-amylose single crystal tilted around its long axis and the tilt angle: a) TEM images of the crystal in longitudinal view tilted around the c-axis. The tilt angles are those of the specimen holder. b) Tilt around the c-axis of the crystal seen in cross section and its corresponding longitudinal projection. For simplicity, only two gray levels have been used to distinguish between the edges and the center of the crystal. c) Corresponding projections of the reciprocal lattice (black dots) along the tilt axis c. The zone axes and theoretical tilt angles are those defined inFigure 4. The crystal cross section is superimposed in grey.

Figure 6 .

 6 Figure 6. Four typical electron diffraction diagrams (left column) from the [hk0] series of zone axes listed Figure 4, recorded by tilting the crystals about their long axis, horizontally oriented with respect to the diagrams. The indexed patterns are given in the middle column. The projections of the reciprocal lattice (black dots) along the tilt axis c are shown in the right column with the cross section of the crystal superimposed in grey. The tilt angles are defined with respect to the plane that contains the a-axis.

Figure 7 .

 7 Figure 7. Scheme describing the orientation of the double helices in the long A-amylose single crystals. The grey cylinders correspond to amylose double helices. The corresponding molecular models of two double helices shifted by c/2 with respect to one another have also been drawn, allowing to localize the reducing end of the amylose chains.

Table 1 .

 1 Comparison of the unit cell parameters and volume V of A-amylose calculated from the data found in various published works. The experimental data have been collected using different diffraction techniques, at different temperatures T.

		X-rays	X-rays	electrons	X-rays	electrons
		(fibers) a	(powder) b	(single crystals) c	(single crystals) d	(this work)
	a (nm)	2.133	2.124	2.076	2.083	2.098
	b (nm)	1.190	1.172	1.116	1.145	1.147
	c (nm)	1.052	1.069	1.045	1.058	1.062
	a (°)	90	90	90	90	90
	b (°)	90	90	90	90	90
	g (°)	123.91	123.5	122.51	122.02	121.46
	V (nm 3 ) e	2.216	2.218	2.042	2.139	2.180
	T (°C)	20	20	-173	-173	-180

Table S1 .

 S1 hkl indices of the set of diffraction spots identified in the diagrams of A-amylose single crystals; experimental d-spacings dobs measured after gold calibration; d-spacings dcal calculated from the unit cell determined with a least-square method; |dobs-dcal| error. The reflections have been sorted by increasing h index.

	-6 3 12	0 -3 -2	6 3 2	0.15231 0.25838 0.16477	0.15222 0.25971 0.16142	0.00009 0.00133 0.00335
	-6 3 12	0 -1 -3	4 5 0	0.19859 0.20317 0.17141	0.19832 0.20316 0.17433	0.00027 0.00000 0.00292
	-6 3 12	0 -1 -3	2 7 2	0.25615 0.14715 0.16298	0.26005 0.14824 0.16564	0.00390 0.00109 0.00266
	-6 3 12	0 -2 -4	0 3 2	0.29500 0.29909 0.16267	0.29826 0.29630 0.16528	0.00326 0.00279 0.00261
	-5 3 12	4 -3 -4	3 1 4	0.22031 0.36022 0.14351	0.22045 0.35958 0.14548	0.00014 0.00064 0.00197
	-5 3 12	3 -3 -6	1 3 6	0.32467 0.25700 0.11835	0.33054 0.25971 0.11821	0.00587 0.00271 0.00014
	-5 3 12	2 -4 -4	1 9 0	0.37422 0.10858 0.17469	0.38043 0.10899 0.17391	0.00621 0.00041 0.00078
	-5 4 13	1 -1 -6	3 0 5	0.26355 0.51784 0.12291	0.26872 0.52301 0.12305	0.00517 0.00517 0.00014
	-5 4 14	0 -1 -6	5 2 4	0.18178 0.37568 0.12638	0.18267 0.37263 0.12607	0.00089 0.00305 0.00031
	h -5 4 15	k 0 -1 -6	l 3 4 3	dobs (nm) 0.25179 0.23545 0.12719	dcal (nm) 0.25170 0.23676 0.12681	|dobs-dcal| (nm) 0.00009 0.00131 0.00038
	-19 -5 4 16 -18 -4 4 17 -17 -4 4 18 -16 -15 -15 -14 -14 -14 -13 -13 -13 -13 -12 -12 -12 -12 -11 -11 -11 -10 -10 -10 -10 -9 -9 -9 -9 -9 -9 -8 -8 -8 -8 -8 -8 -8 -8 -7 -7 -7 -7 -7 -7 -7 -7 -6 -6 -6 -6 3 12 3 11 2 11 2 11 2 10 2 10 2 10 2 10 2 10 1 10 1 9 1 9 1 9 1 9 0 9 0 9 0 8 0 8 0 8 0 8 0 8 -1 8 -1 7 -1 7 -1 6 -1 6 -1 6 -1 6 -2 6 -2 6 -2 6 -2 6 -2 6 -2 6 -2 6 -3 5 -3 5 -3 5 -3 5 -3 5 -3 5 -3 5 -4 4 -4 4 -4 4 -4 -4 4 4	6 0 -1 -6 4 3 -2 -6 4 2 -2 -6 4 4 2 4 2 2 4 2 2 1 3 2 2 1 2 1 0 2 1 1 0 3 2 1 0 0 0 4 3 2 2 1 0 0 0 4 3 2 2 1 0 0 0 4 3 2 1 -1 -1 -1 -6 -4 -4 -2 -2 -2 -6 -2 -4 -1 -4 -1 -4 -1 -2 -3 -1 -2 -2 -2 -3 -1 -3 -1 -3 0 -4 0 -6 0 -4 -2 -4 -2 -2 -1 -2 -1 -2 -2 -1 -1 -4 -1 -2 -2 -6 -2 -4 0 -3 0 -3 -1 -2 -1 -2 0 -2 0 -2 0 -1 1 -1 -2 -1 -1 -1 0 -5 0 -4 0 -2 1 -2 2 -2 -2 -2 0 -4 0 -4 0 -4 1 1 -2 -2	1 1 6 2 6 2 0 1 5 0 2 0 4 3 3 2 8 2 1 7 1 7 0 0 6 6 5 5 3 4 4 2 2 3 3 3 9 3 1 0 2 2 0 2 8 4 2 1 1 3 1 1 7 3 1 2 0 2 0 3 2 1 7 4 1 4 1 2 8 0 4 4 2 2 0 0 2 5 2 5 3 3 5 5 3 1 1 6 3 4 9 2 0 6 4 4 4 6 2 2 0 7 2 3 5 7 5 5 0 3 6 1 2 3 0 2 6 4 4 0 2 2 0 4 4 0 2 8 0 5 1 1 1 3 7 5 7 1 5 1 3 9 1 0 8 2 2 4 0 2 0 4 8	0.11016 0.33724 0.16672 0.12557 0.09657 0.30183 0.47681 0.12230 0.10659 0.47056 0.35682 0.11667 0.11892 0.13021 0.12446 0.14515 0.09782 0.13843 0.16023 0.10882 0.15470 0.10545 0.17195 0.16930 0.12291 0.11863 0.14040 0.13521 0.14798 0.16368 0.15742 0.18011 0.16944 0.19146 0.19467 0.18047 0.10154 0.17301 0.19603 0.23402 0.22742 0.23556 0.25838 0.22534 0.11378 0.17135 0.20541 0.24251 0.27134 0.22381 0.29201 0.27502 0.13016 0.20735 0.24924 0.23612 0.31111 0.28444 0.34271 0.31462 0.15386 0.57817 0.11241 0.20021 0.18658 0.23956 0.18483 0.38680 0.10511 0.58201 0.16395 0.25605 0.19265 0.46457 0.20757 0.95100 0.19467 0.18127 0.18261 0.19899 0.19661 0.29909 0.15519 0.20955 0.19256 0.77109 0.22260 0.17625 0.18764 0.26461 0.09880 0.52781 0.23783 0.16616 0.17720 0.23034 0.18714 0.17531 0.23126 0.46266 0.25610 0.14242 0.22406 0.31366 0.16368 0.14932 0.17562 0.18800 0.19240 0.27570 0.14775 0.91389 0.27205 0.34632 0.31635 0.37962 0.15971 0.23556 0.20929 0.90550 0.28728 0.45694 0.35002 0.25308 0.21272 0.94523 0.28700 0.12446 0.34114 0.18746 0.38567 0.51556 0.22586 0.30463 0.13338 0.19980 0.14409 0.58024 0.18937 0.47681 0.26792 0.11016 0.38079 0.44200 0.12022 0.34034 0.25114 0.22812 0.28692 0.36987 0.51906 0.23400 0.12902	0.10960 0.33918 0.16767 0.12514 0.09673 0.30442 0.47644 0.12133 0.10625 0.47644 0.35463 0.11594 0.11730 0.12999 0.12449 0.14422 0.09739 0.13837 0.15937 0.10854 0.15369 0.10570 0.17433 0.16943 0.12240 0.11887 0.14002 0.13554 0.14783 0.16294 0.15715 0.18302 0.16959 0.19398 0.19346 0.18586 0.10148 0.17337 0.19545 0.23822 0.23172 0.23460 0.26150 0.22471 0.11417 0.17108 0.20615 0.24838 0.27662 0.22875 0.28845 0.27674 0.13048 0.20726 0.24856 0.24116 0.31763 0.29097 0.33887 0.31552 0.15358 0.58194 0.11217 0.19111 0.18521 0.24093 0.18340 0.38956 0.10553 0.57323 0.16163 0.25578 0.19021 0.46387 0.20373 0.95288 0.19236 0.18230 0.18302 0.19818 0.19346 0.29778 0.15663 0.20886 0.19398 0.77913 0.22655 0.17701 0.18724 0.26552 0.09877 0.53104 0.23822 0.16645 0.17732 0.23336 0.18632 0.17419 0.23460 0.46672 0.26150 0.14268 0.22471 0.31731 0.16333 0.14843 0.17330 0.18950 0.19108 0.27054 0.14815 0.91335 0.27259 0.34730 0.31763 0.37710 0.15776 0.23789 0.21106 0.89480 0.29097 0.45667 0.34783 0.25455 0.20900 0.95288 0.28566 0.12447 0.33887 0.18964 0.38472 0.52011 0.22413 0.30445 0.13359 0.20011 0.14219 0.58194 0.18836 0.48232 0.26725 0.11018 0.38043 0.44740 0.12046 0.34215 0.25222 0.22834 0.28660 0.37263 0.52301 0.23194 0.12789 average error	0.00194 0.00095 0.00043 0.00056 0.00259 0.00037 0.00097 0.00016 0.00588 0.00219 0.00073 0.00034 0.00162 0.00384 0.00090 0.00028 0.00653 0.00377 0.00024 0.00652 0.00910 0.00137 0.00504 0.00137 0.00143 0.00068 0.00276 0.00042 0.00009 0.00877 0.00232 0.00032 0.00027 0.00244 0.00172 0.00070 0.00384 0.00356 0.00188 0.00231 0.00494 0.00103 0.00041 0.00528 0.00081 0.00315 0.00587 0.00131 0.00144 0.00074 0.00069 0.00142 0.00027 0.00804 0.00395 0.00039 0.00076 0.00040 0.00062 0.00091 0.00003 0.00312 0.00323 0.00039 0.00096 0.00029 0.00012 0.00430 0.00302 0.00082 0.00420 0.00112 0.00334 0.00058 0.00406 0.00540 0.00036 0.00026 0.00065 0.00006 0.00365 0.00035 0.00539 0.00089 0.00232 0.00121 0.00150 0.00132 0.00252 0.00516 0.00040 0.00015 0.00054 0.00054 0.00291 0.00098 0.00128 0.00027 0.00252 0.00195 0.00074 0.00233 0.00177 0.00015 0.01070 0.00369 0.00033 0.00027 0.00219 0.00038 0.00147 0.00372 0.00024 0.00765 0.00134 0.00051 1.0006e 0.00227 0.00013 0.00218 0.00095 0.00238 0.00455 0.00173 0.00025 0.00018 0.00021 0.00101 0.00031 0.00190 0.00028 0.00170 0.00101 0.00086 0.00551 0.00067 0.00006 0.00002 0.00036 0.00043 0.00540 0.00024 0.00093 0.00181 0.00108 0.00003 0.00022 0.00032 0.00022 0.00276 0.00395 0.00206 0.00113 0.00192

Acknowledgment

This research project has been partly funded by a Marie Curie Early Stage Research Training Fellowship of the European Community's 6 th Framework Programme, under contract n°MEST-CT-2004-503322. We thank P.-C. Escalier (LISBP) for his help in preparing the fractions of synthetic amylose, and D. Dupeyre (CERMAV) for assistance with scanning electron microscopy. The FEG-SEM observations have been performed during a test session organized by JEOL at Consortium des Moyens Technologiques Communs de Grenoble.

Supplementary Material

Determination of 𝐷𝑃 $ ##### and 𝐷𝑃 % ###### from the high-performance anion-exchange chromatography data (HPAEC):

The characterization of the amylose chains contained in the SAA fractions was performed by HPAEC with pulsed amperometric detection (PAD). The operating conditions were described in details by Montesanti et al. (2010). For each DPI, the concentration of maltooligosaccharides Ci was evaluated using the linear relationship between the detector response per mole of a(1,4) chains and its degree of polymerization [Koch et al., 1998]. The linear curve coefficients were determined using maltooligosaccharide standards with a DP ranging from 2 to 7 and were used to estimate the amounts of longer chains.

Number-and weight-average DPs (𝐷𝑃 $ ##### and 𝐷𝑃 % ###### , respectively) and polydispersity index P were calculated as:

.

)

References:

• Montesanti N., Véronèse G., Buléon A., Escalier P.-C., Kitamura S., Putaux J.-L.,

Biomacromolecules 2010, 11, 3049-3058.

• Koch, K., Andersson, R., Aman, P. J. Chromatogr. 1998, 800, 199-206. [110] (-58°)

[120] (-24°)

[250] (-13°)

[130] (-4°)

[140] (+6°)

[160] (+16°)

[010] (+34°)


Fabio Quassoli
email: fabio.quassoli@unimib.it

Monica Colombo
email: monica.colombo@unimib.it

Andrea Molteni
email: andrea.molteni@unimib.it

Governing through security? Institutional discourse, practices, and policies in the metropolitan city of Milan

In our paper, we aim at pointing out the way the most relevant institutional actors currently define the security agenda for the Milanese metropolitan area, which kind of goals they try to pursue, upon which instruments and resources they can rely, which division of labour and forms of cooperation they try to putting into practices. We draw from an analyses of both official documents by the main public institutions involved in the governance of security in Milan and semi-structured interviews to all the members of the Comitato provinciale per l'ordine pubblico e la sicurezzaa board that gather the president of the province, the mayor of the province capital (plus mayors of other cities and towns of the province who can be involved on an ad hoc basis), the representative of the Ministry of Internal Affairs (Prefetto), the District Attorney and the chiefs of all the national police forcesas well as to politicians, civil servants and commissioners of the local police of the city of Milan. We illustrate how discourses and practices of in/security have contributed to the construction of the city as place exposed to a multiplicity of risks that local authorities and police forces are expected to manage. Furthermore, we highlight how the diffusion and legitimization of an 'ideology of safety' has turned the demand to live in safe communities into an attempt to legitimize exclusionary practices insofar as discourses on security were strictly interconnected with discourses on cultural identity and, focusing on both the (imagined) community repertoire and the us/them opposition, ended up legitimizing a racialized urban governance of inclusion and exclusion. Finally, we try to show that a recent attempt, by the new centre-left government, to modify such an approach is generating ambiguous and controversial results and is paradoxically promoting an even stronger securitization of urban policies, spaces and life through more democratically oriented governmental practices.

Introduction

In this paper we intend to illustrate the role that security issues have played in the last two decades with respect to the overall governance of the city of Milan. We want to show how the very possibility of imagining the governance of Milan depends, among other things, on a shared definition of what security is or should be. In addition, we will focus on how the main institutional actors currently shape the security agenda of Milan, looking at the type of goals they pursue and the normative provisions and resources they have, along with the division of labour and the forms of cooperation they seek to implement. Our study is based on original research conducted between 2013 and 2015, in which we examined the most relevant institutional documents produced on this issue by the main public actors, and carried out semistructured interviews (between November 2014 and May 2015) both with members of the Provincial Committee for Public Order and Security -which includes the president of the province, the mayor of the provincial capital (and other mayors convened ad hoc), the Chief of Police and the local heads of all police forces (Polizia, Carabinieri and Guardia di Finanza) -and with a number of officials and executives from Milan's local police force. Special attention was paid to three main thematic areas: a) definitions of urban security; b) the main actors and their functions, competences and responsibilities; c) continuity and changes in the governance of urban security in the Milanese context.

I. Securitization of urban governance

Security has always been a major concern of governments and citizens in Western societies. From its origin, the modern state has prioritised the protection of citizen's safety and their rights to individual property. The prioritisation of safety and private property are seen as a set of "goods" which [START_REF] Castel | L'insécurité sociale. Qu'est-ce qu'être protégé?[END_REF] defines as "civil security". During the 20th Century, this primary form of protection was progressively supplemented by a broader protective function, linked to the effective exercise of social rights through universal access to a set of goods and services essential for full participation in social life. Castel argues that it is precisely in this combination of civil security and social security that we saw the establishment of the pact between governors and citizens that characterised Western liberal-democracies in their socalled trente glorieuses.

This order progressively deteriorated during the 1980s -although in Italy only starting in the 1990s -to the extent that, even in those states that are still the safest on the planet [START_REF] Garland | The Culture of Control: Crime and Social Order in Contemporary Society[END_REF]),1 the concern for the "civil" dimension of security gradually started to impose itself as a salient theme in public debate, alongside the growing erosion of social rights. In Italy in the nineties there was much social alarm around security issues and there was an increase in forms of citizen protestsometimes spontaneous, much more often organized (Della Porta 2004) -in response to the "decay of neighborhoods", the "spread of petty crime" and the presence of social groups (the homeless, irregular migrants, drug addicts, prostitutes, etc.) who were perceived to be dangerous [START_REF] Maneri | Il panico morale come dispositivo di trasformazione dell'insicurezza[END_REF]). For at least two decades, the defense of neighbourhood decorum and the protection of the security of urban spaces have been the main reasons used to call for, and justify, the greater presence of police forces, the installation of devices to control public space (video surveillance), and the implementation of forms of situational prevention. All this is in the name of a local version of the North American brand of a 'zero tolerance policy' [START_REF] De Giorgi | Zero tolleranza: strategie e pratiche della società di controllo[END_REF].

Furthermore, the public debate on security was deeply shaped by the internal logic of the political framework and the relationship with the mass media, in a way largely independent of the emergence of "objective" risks. In fact, in the '90s and the 2000s, empirical evidence from crime statistics painted a highly controversial picture, calling into question any correlation between trends in crime rates and the centrality of the issue of insecurity within public debate [START_REF] Istat | Cento statistiche per il paese[END_REF]European Security Observatory 2009).

This discrepancy was so evident that a crucial distinction between real and perceived insecurity has rapidly emerged both in the political and in the scientific sphere, allowing a partial redefinition of the functions of various levels of government and identifying the local administration as the political-institutional actor that must take responsibility for citizens' sense of insecurity [START_REF] Barbagli | Egregio signor sindaco: lettere dei cittadini e risposta dell'istituzione sui problemi della sicurezza[END_REF].

It is in such a climate that security has transformed from being "public" -i.e. the prerogative of central institutions and the exclusive domain of national police forces -to being "urbanized", thus quickly becoming a central issue on the city government's agenda under the rubric of "urban security". Politicians and administrators begin to enhance their electoral credibility by making promises to do everything in their power, once elected, to "cleanse" urban spaces from all threats to citizens, and to base their government action on policies that openly tackle the issue of security in the city [START_REF] Palidda | Domanda di sicurezza e forze di polizia nei capoluoghi di provincia emiliano-romagnoli, Rapporto di Ricerca, Research report for «Città sicure[END_REF]2000).

The process of the recontextualization of security -which from being "public" has become "urban" -is therefore accompanied by a reconfiguration of urban policies through the widening of the range of risks -i.e. of morally unacceptable and/or criminal behaviour, and of subjects considered to be dangerous -which have to be addressed through security instruments. Grounding the definition of issues pertaining to city governance on the identification of specific threats, behaviours, situations or ethnic groups that supposedly represent a risk justifies the request for urgently implemented exceptional measures. These measures, when implemented through administrative acts such as ordinances against windscreen washers, commercial abuse, begging, the sale of alcohol at night, or campaigns against illegal residential settlements, "Roma camps", and so on, mark the complete securitization of the city's public administration [START_REF] Buzan | Security: A New Framework for Analysis[END_REF]. This is precisely how, during the 1990s and the 2000s, many crucial issues such as traffic, immigration, crime, the suburbs, freedom of religious expression, etc. were gradually brought into the semantic field of urban security [START_REF] Procacci | Le trasformazioni del concetto di sicurezza[END_REF]Marchetti and Molteni 2013, 48). 2

A striking example of the "securitising" of a complex and delicate social issue can be seen in the policies of Milan's centre-right city councils between 1993 and 2011 in response to a fundamental transformation of the urban fabric triggered by the growing presence of foreign citizens in the city. For more than fifteen years, the municipal administration, unlike in many other large European cities, had no policies aimed at fostering the socio-economic integration of migrants, the promotion of their languages and cultures of origin, intercultural dialogue or the economic valorisation of cultural diversity in the city [START_REF] Caponio | Immigrazione, politica e politiche. I casi di Milano, Bologna e Napoli[END_REF]). On the contrary, all efforts were concentrated on creating policies for the "protection of the citizenry" (or rather of Milan's "native" residents and city users) from threats by certain social groups, among which migrants stood out (a group which Bauman described as foreigners ante portas 3 ). The typical pattern, replicated in many areas of the city, was that the newcomers triggered in the old 2 These factors, grouped under the semantic umbrella of urban security, create, according to the mayors of Italian cities, great social alarm (Anci-Cittalia 2012) and are often associated with the behaviour, or mere presence, of marginalised social groups: beggars, people with mental distress, prostitutes, squatters, drug and alcohol users and, in particular, nomads and migrants. Moreover, within this framework urban security, redefined in terms of legitimate needs and rights of the citizenry, has increasingly become a politically neutral issue, as summed up by the slogan: "Security is neither rightwing nor left-wing" [START_REF] Zedner | Security[END_REF]).

3 See Bauman 1997.

residents the feeling of being an encircled minority. This feeling elicited defensive reactions, which led to the formation of neighbourhood committees against degradation and petty crime. Protests of organized residents, fuelled by "moral entrepreneurs", the media and public administrators, legitimised an interpretation of the conflict over the use of public spaces as a non-negotiable opposition between "us" and "them" [START_REF] Marzorati | Non c'entrano niente con la via». Rappresentazioni della differenza e immaginari urbani nella trasformazione commerciale di due quartieri a Milano[END_REF][START_REF] Quassoli | Making the neighbourhood safer: social alarm, police practices and immigrant exclusion in Italy[END_REF]). Instead of mitigating widespread anxieties and fears by bringing them within the scope of "reasonableness", politicians and administrators often gave in to these reactions, leading them to either adopt or call for security policies focused exclusively on the penal-repressive dimension (e.g. orders against multiple forms of anti-social behaviour, large-scale patrolling of public spaces, evictions of illegal settlements, etc.). 4 For example, between 2008 and 2009, eight ordinances were issued in relation to street prostitution, damage to public and private property, alcohol consumption and begging, as well as on the trade and use of drugs. In 2010, seven other ordinances were issued which regulated the opening hours of certain shops (kebab shops and phone centres) in certain areas because they were considered to be high-risk (via Padova, via Imbonati, and the Comasina and Corvetto areas). 5 In the same years, "Operazione strade sicure" (Operation 'Safe Streets') was launched with the 2008 "Security Package" and is still ongoing. It led to the increase and intensification of patrols of the city -although with mixed results. This has led to the creation of mixed patrols composed of police However, these interventions not only failed to address the causes of social hardship, but further fuelled it: on the one hand, they reinforced the perception that the city was actually unsafe, resulting in an increase, rather than a decrease, in a "feeling of insecurity"; on the other hand, they helped to reclassify security as a selective good, surreptitiously or explicitly proposing a notion of citizenship that excluded a significant share of its real citizens, i.e. the poor, the homeless, drug addicts, prostitutes, and migrants, whose citizenship rights were effectively reduced and who were thus disempowered. In this phase, the Milan case seemed to be coherent with a neo-liberal interpretation of the recent transformations in urban governance on a global scale, particularly in terms of the proliferation of local regulations and policies targeting the poor and the informal economy, the strengthening of the role of the police in maintaining order, and the re-emergence of a racialised discourse about the poor that is closely connected to their criminalization. 7 The only aspect that does not fit this interpretation is the strengthening of the role of public institutions traditionally operating in the field of security and the virtual absence of any form of deregulation.

On the contrary, the dual process of the "urbanisation" of security and the "securitisation" of urban governance has led to new forms of cooperation -as well as new opportunities for friction - [START_REF] Pavarini | L'amministrazione locale della paura. Ricerche tematiche sulle politiche di sicurezza urbana in Italia, Roma, Carocci[END_REF] between public authorities operating at the central and local levels. For example, the Minister of Home Affairs established in a special decree (5 August 2008) that urban security should be understood as "a public good to be protected through activities in local communities aimed at fostering compliance with the norms governing civil life, in order to improve living conditions in urban centres, civil coexistence and social cohesion"a definition consistent with the dominant public discourse [START_REF] Selmini | La sicurezza urbana[END_REF]), which potentially extends the scope of security to encompass every aspect of city government.

Moreover, the growing importance given to the governance of urban security, and the consequent attribution of an increasingly important role to local governments in this specific policy field, have favoured a shift in decision-making powers from national to local authorities [START_REF] Menichelli | The national picture: The reconfiguration of sovereignty, the normalization of emergency and the rise to prominence of urban security in Italy[END_REF].8

On the one hand, city mayors, their coordination and representation bodies (the ANCI and the Italian Forum for Urban Security) and, in some cases, ad hoc coalitions (the Parma Charter), have put forward demands for greater autonomy in the security domain, for greater powers and more resources, as well as for greater involvement in the management of security and of the phenomenon of "urban degradation and disorder".

On the other hand, the responsibilities and territorial distribution of powers in the field of public order and security management have gradually been redefined. In 2006, "Local Security Pacts" were agreed between the Ministry of Home Affairs and municipal administrations, with the aim of improving the involvement of local communities in the creation of urban policies through participatory forms of producing the public good. In the case of the province of Milan, the pacts were then converted into formal agreements between the prefetto and the local mayors aimed at strengthening cooperation between national police forces, local police, third sector associations and private individuals, through the promotion of projects aimed at increasing the sense of security in urban areas, improving the quality of life in the city, and encouraging civic participation [START_REF] Colombo | Exploring the intersections between governmentality studies and critical discourse analysis: A case study on urban security discourses and practices[END_REF].

In 2008, following the adoption of the "Security Package" (Legislative Decree 92 of 23 May 2008), this process reached its final stage with an amendment to the law on local administration, which broadened the prerogatives of Italian mayors, authorising them, as government officials, to adopt "necessary and urgent" measures to prevent and address "serious dangers threatening public safety and urban security". 9

In the 2000s the work of the Provincial Committees for Security and Public Order (established by Law 121/1981) 10 gained more visibility and relevance. The Provincial Committees established themselves as an inter-institutional platform facilitating dialogue, coordination, and the 9 At the local level, the 2008 "Security Package" had a primarily symbolic objective, as the realization of a sort of securitarian devolution, with all the emphasis placed, in the political and public debate, on autonomy and on the role of local government (Marchetti and Molteni 2013, 54-56).

10 Participation in the committee has also been extended to include mayors of non-capital cities whenever matters relating to the territories they govern are discussed.

circulation of information and knowledge between all actors with jobs and responsibilities in the field of security within a given area.

II. Urban governance, discourses and security practices in Milan

In light of what has been outlined above, we shall now turn to the salient elements of security governance in Milan that emerged from the fieldwork, with particular reference to the construction of a shared security framework, the relationships between institutional actors operating in the field of security, and the dispositifs that were put into place.

Security: Different nuances, shared premises

A key issue, which relates to the processes of securitisation discussed in the first part and which emerges clearly from the analysis of the interviews, concerns the scope of the application of the concept of security and the degree of consensus over its definition among actors participating in the committee. Two remarks can be made in this regard.

1)

Each actor tends to propose a definition of security that is consistent with the functions that the institution they represent is supposed to perform: there is a shift from a "restricted" notion of security which focuses on activities of a preventive and repressive nature conducted by the national police force -advanced by those who have a "technical" roleto a broader notion of security -held by managers and officials of the municipal police (as well as by some administrators) -which includes aspects related to the degradation of neighbourhoods, to a diverse range of deviant behaviour, to the quality of life in the city and, in one case, to a purely political stance that conceives of security in terms which suggest an ideal of good city governance.

"The concept of urban security is very broad and not always welldefined, and it affects all aspects of society. When we talk about urban security, we refer to the problem of the suburbs, where there are no efficient services, all the way down to security connected to large-and small-scale crime." (Head of Cabinet, Local Police of Milan)

"In a general sense, security is to ensure peace in the city (...). A city is safe when there is no crime, no degradation, when the city is a "paradise". It is clear that this isn't the case in Milan, the larger the city, the harder or more unattainable the dream of having a safe city is." (Chairman of the Committee on Security and Social Cohesion)

Local governments now commonly invoke security concerns, with some paradoxical effects. On the one hand, politicians and administrators seem to have aligned with many sociologists and criminologists in criticising the notion of security as being confined to the criminal and the deviant. As many analysts have stated (Bauman 1997;Palidda 2016;Stefanizzi 2014), the concept of security should be understood in a multidimensional way, and security issues should encompass social issues. In this sense, the institutional actors' frame of reference is quite different from that which characterised the seventeen years of the centre-right administrations (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010)(2011). On the other hand, however, with an increase in the number of issues falling under the umbrella of security (including the constant change in the sociodemographic composition of the population, the transformations undergone by the economic and productive fabric of the city, the conflicts between different groups that compete for the use of public space), the process of securitisation gains momentum [START_REF] Balzacq | Securitization Theory How Security Problems Emerge and Dissolve[END_REF].

"For sure one of the most difficult issues is that of small-scale crime, even if the numbers are down; it is a crime that affects people personally (...) Another aspect of degradation is noise and civil coexistence, as the nightlife in Milan has expanded, leading to the presence of drunken youths and numerous acts of vandalism throughout the year. Another pressing problem in the Milan area is begging, which has been addressed by introducing a policy that provides for an increase in the number of shelters. We have also closed down several Roma camps." (Municipal councillor for security of the City of Milan)

"Milan has some security problems which are typical of metropolitan areas, the problems have increased over time and involve the redevelopment and renewal of peripheral areas that appear less privileged, of neighbourhoods on the outskirts of Milan which demand their fair share of attention, this is a common theme in all great metropolitan areas." (Provincial commander of the Carabinieri)

A heterogeneous set of phenomena are, therefore, redefined as generalised forms of risk, thus reinforcing what Rose described as "risk thinking" (2000, 332), a line of thought which is increasingly widespread in Western societies.11

"Never underestimate anything, this is the right approach. You must be aware of everything and not overlook situations that may be irrelevant at the time but that may escalate. A Prefect needs to be able to identify a problem before it turns into one: signs of potential escalation, so as to act on the risk, not the danger. Anticipating risky situations and carrying out prevention activities to avoid them escalating into a public order emergency". (Prefect of Milan)

Narratives of this kind tend to feed a real "security frustration" [START_REF] Castel | L'insécurité sociale. Qu'est-ce qu'être protégé?[END_REF] and contribute to creating a generalised anxiety about "security", a term that ends up encompassing a wide and varied combination of urban problems and governance practices.

2) According to our respondents, the distinction between objective and perceived security is crucial and is used to qualify the securitisation process. In a city like Milan, which all respondents depict as very safe compared to other large European cities, local administrators seek to improve the perception of security even where real security (understood as the likelihood of being subjected to a crime) cannot possibly be increased.

"Certain types of crime have decreased, while predatory crime, which bothers people most, is a bit on the increase. The reason behind robberies and looting is linked to the economic crisis. I believe that in recent years safety has neither increased nor diminished, despite the opposition trying to paint the city of Milan as the Wild West. (...) Then, but this is well known, it is necessary to distinguish between real and perceived safety, which is equally important. Especially for those in government, the problem that must be tackled is also to ensure perceived safety, i.e. the one citizens regard more subjectively, rather than objectively."

(Chairman of the Committee on Security and Social Cohesion)

Although statistical data indicate a steady and gradual decline in crime, citizens' perception of high insecurity -which is taken as a fact -is traced back to the urban and social transformations that have characterized Milan in recent decades, and is invoked to legitimise heavy-handed and extensive interventions by city administrations aimed at ensuring urban security.

Let us consider, for example, the growing spread of the concept of "participatory security", which entails the active involvement of citizens in the activities of protecting the local area and which is at the heart of the project "Neighbourhood Watch Officers" (vigili di quartiere), promoted by the centre-left municipal administration and officially launched on 3 rd April, 2012.12 Each of the 84 city districts were assigned four neighbourhood watch officers who are deployed at the gates of primary schools, in markets, at neighbourhood events and at crossroads, under the supervision of local officials and assisted by police patrols. They travel by bicycle, are in contact with a coordination centre that can be reached by phone or internet by anyone, and are trained to establish dialogue with citizens in order to become familiar with the daily problems of the city and take timely action to resolve them. The intervention model on which the project was based is characterised as "proactive", that is, "centred on knowledge of the area and on interaction with the inhabitants". In the official website of the project, the "mission" of the neighbourhood watch officers was defined as follows: "A figure who 'cares for' the neighbourhood and who specialises in 'urban well-being', which is not simply about enforcing the rules, but also about sharing critical issues and seeking solutions for a safe and supportive community. For a participatory urban security practiced in everyday life 'together' with the citizenry. For active listening aimed at obtaining credibility, as well as the trust of those living in the neighbourhood".

The main goal of the project is to bring the institutions closer to the citizens, in order to better understand their needs and to identify, with the active participation of stakeholders, the most appropriate shared solutions. The administration regards the project's implementation as a turning point in public security policies, because officers no longer perform only the administrative functions of the municipal police, but are now called upon to contribute to decreasing levels of perceived insecurity. In the discourse of our interviewees, "citizens" are seen as being some of the main agents in the production of security. A fundamental aspect of the cooperation between citizens and the police is the early identification of all factors that can contribute to increasing citizens' (subjective) sense of insecurity. The key point thus becomes the constant monitoring of the demand for security by citizens who are discursively positioned as prosumers of security as a good. Their main duty is reporting, and it is through this activity that they contribute individually to reducing/limiting urban degradation. The model requires citizens to report everything that might pose a threat to the system, conceived of as "their own community". Citizens' participation can also be organised in the form of neighbourhood associations and committees working together to retain control of the area and to maintain public order.

The explicit reference to the concept of community reinforces the idea of a homogeneous in-group, the "Milanesi", who share certain values and a common belonging. The city (the territory), is qualified as "our own". The "citizens" are given an active role in the production of security, which consists, in particular, in reporting to the police cases of urban degradation and "suspects", i.e. people who pose a potential threat to security. In the discourse of the interviewees it is the community ("the citizenry") who perceives these individuals as potentially dangerous, and the presence of the (undifferentiated) 'Other' comes to be seen "almost naturally" as a source of threat.

Actors, inter-organisational relations, and instruments

All of the interviewees stressed the quality of the collaboration established in Milan between the different institutions and police forces that participate in the committee meetings.

"The Prefect plans the public security strategies throughout the province and has coordinating powers in matters of public safety over Prefects of the provinces which are part of the region. The Chief of Police, on the other hand, exercises authority in security matters but on a technical level: he makes the most appropriate decisions to manage an event from a technical perspective. The Prefect gives the basic guidelines on how to handle an event." (Prefect of Milan)

This collaboration foresees a division of labour between national and local police forces and the different institutional actors involved (Chief of Police, police commissioner, mayors), alongside specific forms of cooperation on particularly complex and relevant issues, which the committee regularly includes in the agenda. It also benefits from broad agreement on the priorities and forms of intervention aimed at ensuring the safety of the city. It hinges around methods for controlling each urban area and the people who live in it and/or use it.

"Following the appointment of the new Prefect in August 2013, we have enlarged and reviewed the Committee on Public Safety turning it into a body that meets every week and in which the municipality participates regularly, not only when invited by the Prefect as before.

Inside the committee there is greater sharing of strategies, tasks and objectives and this collaboration between local police and law enforcement agencies has allowed us to review progress on strategic situations and to have common lines of approach." (Municipal Councillor for Security)

The city territory is divided into different areas: nine for the local police, corresponding to the administrative decentralised zones of the municipality; and four for the carabinieri and the state police (with the latter having a greater presence). This creates a spatial distribution of resources aimed at making control total, the presence of law enforcement visible, the allocation of resources optimal, and the coordination work between forces efficient. 13A very sensitive aspect of the relationship between state police and local police concerns the latter's prerogatives. Broadly speaking, the tasks undertaken by the local police are not only those competences attributed to them by law but also those acquired on the ground during the fight against crime. Over the past two decades, the local police have formed specialist investigation teams that have earned them growing appreciation by the Public Prosecutor's Office in a of investigations into serious criminal phenomena. The greater prominence given to this area in the first decade of the 21st Century, however, has been to the detriment of other equally important functions that were traditionally the prerogative of the local police, such as consumer protection, worker safety, illegal trade and construction, and environmental crimes (Palidda 2016). With the change in administration in 2011, this transformation has suffered a setback and today the Milanese local police seem more focused on improving their specific skills in the domain of transport policing (in urban areas) and in administrative policing. However, in our interviews with officials there was a clear desire to continue to also work in the fight against crime by virtue of a presumed greater knowledge of the territory, acquired thanks to the constant dialogue with citizens.

"The local police do exactly what it's supposed to do under the rules and codes, and therefore it has a wide remit: we are directly responsible for administrative and traffic police duties. There are differences between the tasks of the Local Police, the Judicial police and the carabinieri, but let's say, it's not so much a legal issue as a question of competence and trust between us and the local administration. As a rule we deal with small-scale crime, while for large-scale crime and more specific issues that require certain skills, the exclusive action of other law enforcement agencies is requested. (...) today the Local Police is centres, remain centralised (or have been re-centralised in recent years, as in the case of the local police in Milan), which is also due to the potential and efficiency of the electronic technologies employed.

used to solve problems that were previously assigned to the police and the carabinieri." (Head of Cabinet, Local Police of Milan) The local police have been particularly eager to take on this new role in relation to operations characterised by high public and media visibility, such as major operations to combat crime in some districts, large events, street demonstrations, evictions, etc. These operations have led to the establishment of thematic working groups, convened ad hoc on the occasion of particular events, as well as territorial working groups for coordination between forces, which reproduce, in areas of administrative decentralisation and at an immediately operational level, the collaborative methods practiced at the provincial (now metropolitan) level by the Provincial Committee for Order and Public Security.

"At the behest of Chief of Police (...) for about two years now, every month, at our station we have been calling a so-called multi-police meeting, to tackle problems that are a bit more complex than ordinary ones. It is attended by the local police and the various heads of the area's police stations, the Carabinieri and the Guardia di Finanza. At this meeting, which usually takes place once a month, we discuss certain, somewhat more serious issues (...). There have also been several occasions when, in order to deal with specific problems, similar meetings have been set up, other than the monthly multi-police coordination meetings, which involve the Councillor, the citizens' committees and representatives of law enforcement agencies in the area, just to understand and agree on the necessary measures to solve a problem.

" (Local Police -area 8 Station)

Action in the field of security is embodied in some dispositifs which, according to Foucault (1977), are to be understood as systems of relations between heterogeneous objects (discourses, practices, artefacts, texts, standards, institutions, administrative measures, quantifications, etc.) which reflect a political urgency or an emergency and constitute the space within which a discourse acquires meaning and produces effects. One of these effects is to give visibility to particular objects, places, situations, behaviours and social groups, in order to control, regulate and govern them [START_REF] Rabinow | Anthropos today: Reflections on modern equipment[END_REF]. We can identify three fundamental dispositifs for the control of the territory of Milan which allow the collection, quantifying, mapping, distribution and making visible of events for which priorities and plans are subsequently defined -ordinances, video surveillance, and risk maps.

As far as ordinances are concerned, which were the main instrument of Milan's political and administrative governance in the domain of urban security in the first decade of the 2000s, it is apparent that the Pisapia administration (2011-2016) marked a strong discontinuity with the past.

In fact, the use of ordinances was greatly reduced, avoiding the bending of extraordinary measures to everyday tasks and limiting their use to situations characterised by urgency, unpredictability and temporariness.

Strong continuity, however, has emerged with regard to the massive and widespread use of video surveillance activities, which did not decrease with the establishment of the centre-left administration. Not only has the number of cameras increased, but video surveillance has maintained a central place in public discourse about security governance in the city.

"The number of CCTV cameras has grown substantially and they perform the function of increasing perceived safety, though they are no deterrant." (Chairman of Committee on Security and Social Cohesion)

In the answers of our interviewees, security cameras -with their visibility and materiality -seem to have a primarily communicative function, that of reassuring citizens, responding to their anxieties of security and their supposed perception of insecurity. In more general terms, however, the use of cameras -the choice of where and how to place them and direct them according to events and occasions -is an expression of governmental rationality.

"Another very important element is the cameras, we have about 1,700 cameras in the city connected with our operation units, we have defined a protocol with the prefecture and with all law enforcement agencies and we have connected the system so that our cameras are viewed and can be operated simultaneously by all law enforcement agencies and the prefecture. This means that it is a system everyone can benefit from, and, in fact, it has improved the effectiveness of our work. These cameras do not work as early warning signals but are critical to investigate crimes and because citizens just need to see the cameras and they somehow feel more secure and protected by the institutions." (Municipal Councillor for Security)

The cameras do not only perform the communicative function of reassuring citizens, or serve only as tools for investigation, repression and punishment through ensuring the identification of those who commit acts that are deemed unlawful. The strategies that support and justify their use, in fact, are based on processes and mechanisms of classification that guide and organise the collection and management of information [START_REF] Cole | Suspect Identities: A History of Fingerprinting and Criminal Identification[END_REF][START_REF] Harcourt | Against Prediction: Profiling, Policing, and Punishing in an Actuarial Age[END_REF][START_REF] Simon | Governing Through Crime: How the War on Crime Transformed American Democracy and Created a Culture of Fear[END_REF], helping to identify specific social groups and situations to be subjected to particular control regardless of their actual behaviour, as well as to define, in every place in the city and in every situation in urban life, "who should be present, where and when, who is 'out of place' and who it is appropriate to see" (Lyon 2007, 94).

Another instrument at the disposal of the police forces, which is widely used in the planning of security governance in the city, are "risk maps", a sort of representation of criminal life in Milan which, through the analysis and visualisation of georeferenced data, detects criminal hotspots and subdivides the territory on the basis of the presumed dangerousness of an equally presumed greater risk, whether general or specific (relative, that is, to a particular type of crime). The sharing of the recorded data and the analyses carried out, presented in the meetings of the provincial committee, end up constituting the technical artifacts whereby decisions on the protection of urban security are made and through which preventive police interventions on the ground are planned.

"We have our own, formalized risk map, we have analyzed a series of filtered data in very specific contexts in order to get, as a local Police, a clear picture of the Milan area which can provide useful guidance for immediate action by the police forces. It is constantly updated on the basis of our information. Through the use of data, images and video a specific situation can take shape and this allows us to divide the city into sectors so as to position the various law enforcement agencies based on their specific responsibilities. Once a problem has been identified, the effort of the police forces is intensified and, after a short time, we can determine whether the problem has been dealt with positively. This, in all cases, has proven to be highly effective, from dealing with urban security, to managing Roma camps, in (facing) conflicts and tensions." (Head of cabinet, Local police of Milan)

In general, these risk assessment tools are based on situational prevention models, depend on the ability to collect and act upon information analysed with actuarial instruments, and are aimed at the examination and probabilistic identification of criminal behaviours and places with the highest risk of victimisation [START_REF] Braga | Policing Crime and Disorder Hot Spots: a Randomized Controlled Trial[END_REF]National Institute of Justice 2005;[START_REF] Yang | Assessing the Spatial-Temporal Relationship Between Disorder and Violence[END_REF]). These technological tools make clear how the actuarial approach [START_REF] Harcourt | Against Prediction: Profiling, Policing, and Punishing in an Actuarial Age[END_REF] based on the notion of risk has become crucial in the governance of cities and constitutes "an effort to depoliticise public issues, to suggest technical solutions to often complex phenomena" (Borraz and Le Galès 2010, 26). Finally, it is evident how the attribution of risk profiles -in other words, different levels of criminal probability -to subjects and social groups [START_REF] Castel | From dangerousness to risk[END_REF][START_REF] Rabinow | Marking Time: On the Anthropology of the Contemporary[END_REF][START_REF] Rose | The Politics of Life Itself: Biomedicine, Power, and Subjectivity in the Twenty-First Century[END_REF]) through the use of technologies and instruments geared towards the identification, classification and governing of individuals, groups, situations and places means obliterating any consideration of the social causes of crime and ends up reinforcing negative stereotypes about particular social groups and urban areas.

III. Expo 2015

In the course of this research, safety management for the Universal Exposition, which was held in Milan in 2015, has repeatedly emerged as a major issue.

The organisation of the security system for Expo 2015 -which was on the agenda of the meetings of the provincial committee over several months -was long and complex, and was based on an attempt to carry out "total planning" -as it was defined by the provincial commander of the carabinieri -that would not overlook any possible risk.

Expo played an important role in the reorganisation of the system and forms of security governance in the Milan metropolitan area in at least three ways: first, the planning and transformations of the concepts, organisational forms and instruments of security governance in the territory; secondly, the resulting long-term transformations; thirdly, the practical consequences and impact on the local security system. In this context, we would particularly like to make a few remarks on the first aspect. As explained by the Milan Chief of Police, the thematic working groups tasked to implement the safety management system at Expo 2015 under his coordination in the months preceding the Expo, prepared, imagined and examined, "all possible critical scenarios and management strategies to address them". On that occasion, "possible" scenarios were projected on the basis of experience gained in local security governance, comparison with the experience of other countries in managing major events, and the specific local situation.

For the London Olympics in 2012, the Rand Corporation developed a model for planning security systems that is particularly relevant in this respect. The model was based on projecting "all possible future scenarios" of security risk, on the assumption that, given the intrinsic indeterminacy of these future scenarios, the organisation of security "must be developed under conditions of great uncertainty". The local authorities whom we interviewed who participated in the Provincial Committee for Security and Public Order said that they were also aware of the fact that "anything could and that therefore absolute planning was impossible. What was needed, then, was the organisation of a system based on the ability to imagine anything that might happen -even without an accurate assessment of the probability of each scenario -and, at the same time, capable of taking action even when faced with the unpredictable. This represents a "style of thought" [START_REF] Fleck | Genesis and Development of a Scientific Fact[END_REF][START_REF] Rose | The Politics of Life Itself: Biomedicine, Power, and Subjectivity in the Twenty-First Century[END_REF] based on an overabundant construction of scenarios and the unpredictability of threats to security, and marks a shift from a logic of prevention to a logic of precaution, in which "security risks proliferate and exceed the ability of authorities to fully manage them, or even to detect them, with the consequence that maintaining the appearance of absolute security becomes an urgent task" (Boyle and Haggerty 2009, 262). Indeed, the focus was on the development of "government technologies" [START_REF] Rose | Political Power beyond the State: Problematics of Government[END_REF] capable of ensuring the objective of managing all those security problems that could not be predicted or prevented, and upon which it was essential, according to the Milan Chief of Police, to intervene quickly and decisively, avoiding any confusion of roles while ensuring effective decision-making and coordination.

The organisation of the management of emergencies that could have undermined the safety of Expo 2015 (in the exhibition site, but also in the city in general) involved setting up two coordination centres: the Joint Operations Centre, a joint control body, and the Emergency Coordination Centre, an operations body tasked with coordinating the interventions of all of the operators involved and with taking immediate action if needed.

So Expo 2015 ended up becoming, in the words of the Chief of Police, a laboratory for experimenting with new approaches to urban security management. The types and means of cooperation between public actors and police forces involved in security management in the metropolitan city have consequences that extend "well beyond what occurs on the days of any individual happening. Mega-events foster a legacy of knowledge, networks and habits that have a bearing on the lives of considerably more individuals than those in attendance" (Boyle and Haggerty 2009, 265). Together with allowing for the setting up of new tools and for experimenting with different forms of joint coordination, Expo 2015 it has been a testing ground for new models of safety management. The emphasis placed on the ability to construct multiple scenarios -virtually all of those imaginable -that would enable a response to any threat, identified not so much in terms of their probability as in terms of their mere possibility, sustained the production of new instruments for the coordination and governance of urban security, based on the ability to intervene and manage, if not foresee and prevent, any situation of danger or disturbance to public order, even extremely unlikely ones. This desire for protection from the unpredictable obviously echoes with the fear that has gripped Western cities and societies since 9/11, and unveils the dream of an ideal city that, if it cannot be purified of every risk or threat, can at least be put perfectly under control.

Concluding remarks

We have tried to illustrate the most recent transformations in urban security policies in Milan, and their continuity/discontinuity with those adopted by previous administrations. The essential elements that emerge from our analysis on the evolution of the discourse and on the policies on security in Milan can be summarised as follows.

Firstly, in line with what has happened in other large European cities over the last two decades, many of the major issues on the city's governing agenda have been placed under the "semantic umbrella" of urban security. This has triggered the profound reconfiguration of a heterogeneous complex of practices, institutions and devices aimed at identifying and governing new forms of generalised risk, together with the redistribution of responsibilities among national and local institutions operating in the field of security. The increasing securitisation of urban life has also led to a shift -both in emphasis and resources -from a concept of city government focused on the need to address a range of social problems to one focused on situational prevention and the criminalisation of problems, conflicts and groups.

If, on the one hand, the centre-left administrations in office since 2011 have tried to distance themselves from what happened in the previous fifteen years -during which problems and policies traditionally understood from a social perspective were approached as security issues -on the other hand, securitisation remains a crucial framework for the government of the city. A double question could be raised concerning this point: the first and more immediate one is to which extent can we conceive the securitization of some core urban issues as an established crucial framework for city governance also in other European cities; the second one stems from the fact that if securitization constitutes a shared element between center-left and center-right coalitions, then the only distinctive elements of the center-left governments seem to be a definition of security that combine criminal and social issues, together with a greater capacity to provide a policy response, in terms of output, effectiveness, and ability to manage the relationships between central and local public institutions.

Secondly, the dominant public discourse on security has definitely embraced the distinction between objective risks and subjective perception, in order both to promote local government as the main political-institutional actor that must take charge of citizens' sense of insecurity, and to strengthen the powers of (national and local) police forces against the (objective and/or perceived) threats that endanger public security in urban contexts. Moreover, the emergence of a risk thinking mindset, together with the importance attached to the perception of insecurity and the involvement of citizens in practices of a governmental nature (McIlvenny, Zhukova Klausen and Bang Lindegaard 2016), continues to entail the serious risk of the selective exclusion of social groups which are seen as problematic. If during the centre-right governments, for example, the issue of the presence of foreign people was directly and explicitly presented as a threat to security, without any attempt to hide the racist undertones and the discriminatory effects of such a discourse, with the centre-left administrations the tone has become milder, although the presence in public spaces of individuals or groups considered as a problem by -and for -the citizenry continues to be associated with the perception of insecurity. 14 Thirdly, the traits that had marked the city's governance in a neo-liberal sense in the previous fifteen years have diminished markedly. If, on the one hand, the direct and explicit criminalisation of marginal and "problematic" social groups has disappeared, on the other hand, the partial securitisation of urban governance has represented an opportunity to further revive the role of public institutions which, despite new forms of division of labour between local and national 14 The same applies to the presence of nomad camps, which are mostly identified as both an actual threat and a significant element in the growth of the perception of insecurity and the disturbance of order and decorum in the neighbourhoods where they are set up.

institutions, maintain a substantial monopoly in the field of urban security. 15Finally, the shift from a logic of prediction to a logic of precaution that has become clear in the organization of security for EXPO 2015 has involved a blurring of the boundaries between policing, which concern public order and security in civil contexts, and a more military approach according to which: "if we cannot know with certainty, the prudent thing to do is to prepare for the worst" (Amoore and de Goede 2008, Bourne 2013). It is reasonable to imagine that such an approach, which has increasingly marked internal and external security policies in Western countries after 9/11, has become more and more relevant also at the level of urban policies in light of the terrorist attacks that hit some of the most important European cities over the last three years (Paris, Manchester, London, Nice, Berlin, Barcelona, to name only the most relevant), making even more blurred the boundaries between police functions and those performed by the army that is increasingly deployed in urban spaces. 16 Furthermore, if global events/threats are both a lab and a turning point for a concerted security governance of the big cities and if do they stimulate an approach based on a logic of precaution we can ask to what extent the latter is reshaping also more ordinary security practices and arrangements in Europe.

Bibliographical references

Amoore, L. and de Goede, M (eds.) ( 2008), Risk and the War on Terror, London, Routledge.

This process started well before concerns about the threats coming from international terrorist networks monopolised the attention of public opinion and the security apparatus.

See :

See Amster, 2003;[START_REF] Caldeira | City of Walls: Crime, Segregation and Citizenship in São Paolo[END_REF][START_REF] Herbert | Conceptions of space and crime in the punitive neoliberal city[END_REF][START_REF] Robins | At the limits of spatial governmentality: a message from the tip of Africa[END_REF][START_REF] Samara | Policing Development: Urban Renewal as Neo-liberal Security Strategy[END_REF][START_REF] Wacquant | Punishing the Poor: The Neoliberal Government of Social Insecurity[END_REF]

Urbanization of security, together with the territorial reorganization of public powers and the emergence of the local/urban as the reference point for policies are perfectly in line with a broader trend of territorialisation that affected, in the same years, many areas of public intervention in Italy[START_REF] Bifulco | Citizenship and governance at a time of territorialization: The Italian local welfare between innovation and fragmentation[END_REF]) and that involved a rescaling of statehood[START_REF] Brenner | New State Spaces: Urban Governance and the Rescaling of Statehood[END_REF][START_REF] Gualini | The rescaling of governance in Europe: new spatial and institutional rationales[END_REF], a reframing of public action in terms of resources, targets and actors[START_REF] Governa | Territories in action, territories for action: the territorial dimension of Italian local development policies[END_REF], as well as a cooperation between public authorities, third sector associations and private actors in both policies' design and implementation.

On risk as a cultural category see[START_REF] Douglas | Risk and Culture: An Essay on the Selection of Technical and Environmental Dangers[END_REF]; on social/securitarian dialectics see[START_REF] Bigo | Illiberal Practices of Liberal Regimes: The (In) Security Games[END_REF] 4-59; on fear as a central element of political debate and government action seeFuredi 2008;[START_REF] Simon | Governing Through Crime: How the War on Crime Transformed American Democracy and Created a Culture of Fear[END_REF]

For a description of the project see: http://www.comune.milano.it/wps/portal/ist/it/servizi/polizialocale/vigili_of_ the_neighborhoods

The subdivision of the territory, however, does not fully correspond to a decentralisation of functions, given that some, in particular those of the coordination of the patrols of rapid intervention entrusted to the operative

For an interesting attempt to delimit and qualify the explanatory scope of the neo-liberal paradigm, see Le[START_REF] Galès | Neoliberalism and Urban Change_Stretching a Good Idea Too Far[END_REF].

On this point, see Amoore and de Goede (2008) and de Goede (2011). As for Milan, we cannot yet provide convincing empirical evidence, as we are carrying on a follow-up right on this aspect.

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