Virginie Renson
email: vrenson@vub.ac.be

Nathalie Fagel

Nadine Mattielli

Serge Nekrassoff

Maurice Streel

François De Vleeschouwer

Roman road pollution assessed by elemental and lead isotope geochemistry in East Belgium

The ability of inorganic geochemistry to record environmental change and especially human impact has been evidenced by several studies across Europe, especially in peat, where it is possible to record the impact of agriculture, mining and other industries. However, despite the numerous investigations on the impact of ancient human activities such as ore mining and smelting, little attention has been paid to geochemistry as a tool to solve problems of palaeopollution in the surroundings of archaeological sites. This paper presents geochemical evidence of the impact of a possible early Roman road built in SE Belgian peatland. Increased Zn and Pb concentrations suggest that Pb-Zn ores were transported on the road. Lead isotope analyses suggest that these ores are locally derived, being compatible with those found in the nearby Pb-Zn ore deposits from East Belgium. Present results provide direct evidence that East Belgian Pb-Zn ores were already being mined during Roman times, i.e. earlier than previously suspected (i.e. 14th century) and that Zn appears to be relatively immobile here. On a broader scale, it also demonstrates that such an early road already had an impact on the environment in terms of metal pollution. This paper enlarges on the range of possibilities offered by geochemistry in the field of geoarchaeology.

Introduction

The Hautes Fagnes plateau (SE-Belgium) consists of a large and discontinuous wetland made of fen, mire and rarely bogs (Fig. 1A). It has provided a key site in studies investigating human occupation and environmental impact in the region since the Celtic civilisation [START_REF] Remy | Monographie archéologique Commune de Vielsalm[END_REF][START_REF] Damblon | Les dépôts tourbeux et l'histoire de la végétation sur le plateau des Hautes Fagnes (Belgique)[END_REF][START_REF] Graillet | De l'or en Ardenne[END_REF]De Vleeschouwer et al., 2007). Interestingly, this area is also located nearby Pb-Zn ores that are known to have been mined since the 14th century [START_REF] Dejonghe | Atlas des gisements plombo-zincifères du synclinorium de Verviers (Est de la Belgique)[END_REF].

The Hautes Fagnes plateau is crossed by a 6-km cobbled road, in a NW-SE direction (Fig. 1A), which is now partly covered by peat. Historical [START_REF] Remy | Monographie archéologique Commune de Vielsalm[END_REF][START_REF] Graillet | De l'or en Ardenne[END_REF] and palynological [START_REF] Dalemans | La Via Mansuerisca, enfouie dans la Fagne des Wez, est mérovingienne, pas romaine[END_REF]) data suggest that it was used as a thoroughfare up to the 13th century although the age of its construction, function and its intended route have always been a matter of debate (e.g. Corbiau, 1981a,b;[START_REF] Dalemans | La Via Mansuerisca, enfouie dans la Fagne des Wez, est mérovingienne, pas romaine[END_REF].

The cobbled road crossing the Hautes Fagnes is recorded in several historical texts and the archaeological remains were discovered in 1768 (see [START_REF] Nekrassoff | La via Mansuerisca, route romaine des Fagnes Le poids de la tradition[END_REF]. The first detailed description of the road was made by [START_REF] Bastin | La Via Mansuerisca[END_REF], who discovered a multi-layered wooden structure which was thought to form the foundation for the cobblestones on the waterlogged peat (Fig. 1B). Such a structure is not found where the road is crossing non-peaty doi:10. 1016/j.apgeochem.2008.06.010 sediments (Corbiau, 1981a) as this kind of wood basement is not necessary to support the road when the substratum is not waterlogged. From base to top, this bearing beechwooden structure was composed of three parts: (1) a set of beams perpendicular to the road, (2) girder/side frame parallel to the road and fitted into the beams, (3) an assembly of unhewn timbers lying perpendicular to the road. The cobbling overlying the wooden foundations is composed of quartzite blocks from the Revin group (Cambrian), a rock common as erratic blocks on the Hautes Fagnes plateau. Finer sediments of variable grain-size ranging from clay to fine gravel are scattered between the cobbles. Given these particular structural and compositional characteristics, although without any age-dating control, [START_REF] Bastin | La Via Mansuerisca[END_REF] attributed a Roman origin to the road. Much later, Corbiau (1981a) carried out three new excavations in the northern part of the road where it was built across a very thin peat layer or on non-peaty sediment (Fig. 1A). The alder-wooden structure at these excavations was either missing or consisted of a single unhewn timbers assembly under the cobblestones. Wood fragments were radiocarbon dated to a period between the 5th and the 8th centuries AD (Damb-lon, 1994). Therefore, Corbiau (1981a) advocated a Merovingian age for this part of the road. This younger age was not contradictory with the estimation of [START_REF] Bastin | La Via Mansuerisca[END_REF], as Corbiau (1981a) mentioned that these new excavations could be non-contemporaneous from those previously studied. Three wood fragments kept from the excavations of [START_REF] Bastin | La Via Mansuerisca[END_REF] were later radiocarbon dated and also provided contradictory age-dating of BC 170, BC 248 [START_REF] Lewalle | La Via Mansuerisca[END_REF] and AD 550 ± 50 (Corbiau, 1981a) that were never discussed. Subsequently, [START_REF] Dalemans | La Via Mansuerisca, enfouie dans la Fagne des Wez, est mérovingienne, pas romaine[END_REF] did a palynological investigation of four cores from the southernmost site studied by Bastin (Fig. 1A) in an attempt to constrain the age-dating of the road construction. They assigned the first impact of the road to small eroded quartzite fragments found in the peat. Using this proxy for the lowest level of the road, these authors compared the pollen record with that of [START_REF] Persch | Zur postglazialen Wald-und Moorentwicklung im Hohen Venn[END_REF] and estimated the building of the road to have occurred around AD 700 [START_REF] Dalemans | La Via Mansuerisca, enfouie dans la Fagne des Wez, est mérovingienne, pas romaine[END_REF].

The possible destination of the road was also thoroughly discussed. In the middle of the 19th century the cobbled road was considered to be part of a Roman road [START_REF] Cauet | Genetic study of Belgian lead and zinc mineralizations in carbonate environments through lead isotopic geochemistry[END_REF][START_REF] Dejonghe | Zinc-lead deposits of Belgium[END_REF], the cobbled road and the various excavations (after Corbiau, 1981a). Peat thickness reported from [START_REF] Wastiaux | Topographie de surface et de subsurface des zones tourbeuses des réserves naturelles domaniales des Hautes Fagnes[END_REF]. (B) Sketch of the findings from [START_REF] Bastin | La Via Mansuerisca[END_REF] redrawn by [START_REF] Mertens | Les routes romaines de la Belgique[END_REF].

linking the cities of Maastricht and Trier (Corbiau, 1981b). Later on, it was associated to a Roman road called Via Mansuerisca, which has been cited in historical texts since 670 AD (Corbiau, 1981b). Several tracks were proposed to link the cobbled road to Trier or to the Köln-Trier Roman road. However, as stated by Corbiau (1981b) these tracks are still hypothetical. Systematic archaeological investigations are needed as despite these numerous studies, the age of the road and its purpose and destination, which may be crucial factors in determining its age, are still under debate.

Moreover, of wider interest, it is well known that the Romans built the first extensive road web across Europe. First built for military purposes, these roads were further developed for trade purposes [START_REF] Chevallier | Les voies romaines[END_REF]. In Belgium, the Roman road system was extended ca. 20 BC, mainly for the defence of northern borders against possible Barbarian invasions, but also for political purposes and for trade between the different cities [START_REF] Corbiau | L'organisation routière du Nord de la Gaule. Regards sur le territoire belge[END_REF]. At the Roman Empire apogee, roads covered 150,000 km [START_REF] Chevallier | Les voies romaines[END_REF] throughout Europe. The environmental impacts provoked by such an intense and modern road web has however never been investigated.

Roman road engineers generally avoided any wetlands, river overbank and inundation plains [START_REF] Chevallier | Les voies romaines[END_REF]. For these reasons, to the authors' knowledge, apart from one other site in Austria (via Claudia Augusta near Lermoos city), the archaeological site described here is unique for the Roman Empire. Indeed, due to its construction in a peatland, the road is very well preserved. Moreover, it offers a unique opportunity to study possible pollution that could be recorded in the surrounding peat accumulation.

In order to answer the various historical, geographical and environmental questions mentioned above, the geochemical and Pb isotopic records in two peat columns taken alongside the cobbled road have been studied. These analyses are accompanied by radiocarbon dates. Local problems discussed in the present study are (1) documenting the purpose of such a road by placing it in a geographical and historical context, (2) providing new clues to better constrain the age of its construction and (3) providing an age of possible early Pb-Zn mining in Belgium. On a broader scale, this study also (1) assesses the environmental impact of such early roads and (2) discusses Pb and Zn mobility in peat.

Using geochemistry in geoarchaeology

Elemental geochemistry and Pb isotope analyses have been successfully used for investigations of peat sequences to reconstruct pollution chronologies in Europe (e.g. [START_REF] Brännvall | The medieval metal industry was the cradle of modern large-scale atmospheric lead pollution in northern Europe[END_REF][START_REF] Martínez-Cortizas | Atmospheric Pb deposition in Spain during the last 4600 years recorded by two ombrotrophic peat bogs and implications for the use of peat as archives[END_REF][START_REF] Novak | Origin of lead in eight Central European peat bogs determined from isotope ratios, strengths, and operation times of regional pollution sources[END_REF][START_REF] Shotyk | Anthropogenic contributions to atmospheric Hg, Pb and As accumulation recorded by peat cores from southern Greenland and Denmark dated using the 14[END_REF]Le Roux et al., 2004a). Contaminant metals, particularly Pb and Zn, linked to mining and smelting activities, have been monitored at various European sites including West Germany, (e.g. [START_REF] Kempter | The local nature of anthropogenic emission sources on the elemental content of nearby ombrotrophic peat bogs, Vulkaneifel, Germany[END_REF], Switzerland, (e.g. [START_REF] Shotyk | Anthropogenic contributions to atmospheric Hg, Pb and As accumulation recorded by peat cores from southern Greenland and Denmark dated using the 14[END_REF], France, (e.g. [START_REF] Baron | Record of metal workshops in peat deposits: history and environmental impact on the Mont Lozère Massif[END_REF] and East-Belgium, (e.g. [START_REF] Sonke | A chemical and mineralogical reconstruction of Zn smelter emissions in the Kempen region (Belgium), based on organic pool sediment cores[END_REF]. In some cases, early pollution could be evidenced, especially if the polluting source was in the vicinity of the study site, (e.g. [START_REF] West | Heavy metals in Holocene peats from South West England: detecting mining impacts and atmospheric pollution[END_REF][START_REF] Mighall | Geochemical evidence for atmospheric pollution derived from prehistoric copper mining at Copa Hill, Cwmywtwyth, mid-Wales[END_REF][START_REF] Baron | Record of metal workshops in peat deposits: history and environmental impact on the Mont Lozère Massif[END_REF]. Previous research dealing with pollution histories in Belgium have been carried out in ombrotrophic bogs from the Hautes Fagnes plateau, SE-Belgium [START_REF] Kempter | Der Verlauf des anthropogenen elementeintrags in Regenwassermoore des westlichen Mitteleuropas während des jüngeren Holozäns[END_REF][START_REF] Gérard | Suivi des apports atmosphériques en plomb au cours de l'Holocène: Enregistrement dans des tourbières des Fagnes[END_REF][START_REF] Goormaghtigh | Suivi des apports atmosphériques en métaux lourds durant la période Subatlantique (depuis 850 ans), dans un milieu continental pollué: enregistrement de deux tourbières des Hautes Fagnes[END_REF]De Vleeschouwer et al., 2007) and peaty sediments [START_REF] Sonke | A chemical and mineralogical reconstruction of Zn smelter emissions in the Kempen region (Belgium), based on organic pool sediment cores[END_REF]. These studies showed that anthropogenic impact dated back to early Roman times.

In the specific field of geoarchaeology, little attention has been given to the potential of tracing past pollution using geochemistry [START_REF] Mighall | Using bog archives to reconstruct palaeopollution and vegetation change during the late Holocene[END_REF][START_REF] Nriagu | A history of global metal pollution[END_REF]. However, previous studies have successfully demonstrated the potential of this approach, (e.g. [START_REF] Elmaleh | A heavy metals record from the ancient northern harbor of Tyre (Lebanon)[END_REF][START_REF] Grattan | The local and global dimensions of metalliferous pollution derived from a reconstruction of an eight thousand years record of copper smelting and mining at a desert-mountainfrontier in southern Jordan[END_REF][START_REF] Baron | Record of metal workshops in peat deposits: history and environmental impact on the Mont Lozère Massif[END_REF]Le Roux et al., 2004b). To the authors' knowledge, this study constitutes the first investigation of environmental impact due to road use during the Roman Empire. It provides a good example of how geochemistry can be used as a tool to broaden knowledge in the role that early civilisations played on the environment.

Materials and methods

Coring and subsampling

In July 2004, an archaeological excavation was carried out by the ''Direction de l'Archéologie du Ministère de la Région Wallonne" [START_REF] Corbiau | Nouvelles recherches archéologiques pluridisciplinaires sur le parcours de la voie médiévale dite la Via Mansuerisca et découverte d'un véhicule dans la Fagne Rasquin à Waimes (Lg)[END_REF] a few tens of metres from the original site studied by [START_REF] Bastin | La Via Mansuerisca[END_REF]. Fig. 2A shows a cross-section of the excavation. The 30-cm thick peat covering the road was removed and a 1.2-m deep trench was dug in the southern section of the road, perpendicularly to its direction. The revealed road structure (Fig. 2A) was similar to the section previously studied by [START_REF] Bastin | La Via Mansuerisca[END_REF]. The peatland is developed on a slight slope. It is now partly fed by small eastward surface streams.

Two peat columns (CR1, downhill and CR2, uphill; Fig. 2B) were collected in the trench on each side of the road using plastic U-boxes (20 cm  10 cm  6 cm). CR1 and CR2 measure approximately 103 cm and 125 cm long, respectively. An undisturbed 2 cm-thick slice was cut along the side of each block and impregnated with resin. The peat blocks were then cut into 1-cm thick slices with plastic tools. Note that 0 cm is at the bottom of the cores.

As there is surface runoff, any possible environmental impact of the road should be more accurately recorded down slope. Therefore, most of the results were obtained on CR1.

Thin sections

Thin sections were made using the method described in [START_REF] De | High resolution petrography on resin-impregnated Holocene peat columns containing tephras. Principle, applications and perspectives[END_REF]. The peat slices were freezedried under high vacuum (6-8 mbar) and impregnated with resin under low vacuum (700-1000 mbar). Polymerisation was achieved in a drying-oven (40 °C, 72 h) and then under laboratory conditions (100 h). Blocks were then polished and thin sections were prepared.

Geochemistry

One-cm thick slices of peat were freeze-dried and milled in an agate jar pulverisette (400 rpm, 1 h). Pellets were prepared by pressing 3 g of peat powder (200 kN/ cm 2 ). The following elements were analysed using X-ray fluorescence (ARL 9400 XP, URPGE, ULg): Si, Al, Ca, Na, K, Zn and Pb. Thirty-nine and 46 samples were analyzed in CR1 and CR2, respectively. International reference material such as coals (CLB-1, NIST 1632b), lichen (BCR-482), pond sediments (NIES-2), tea leaves (NIES-7), exhaust particles (NIES-8) and marine sediments (JSD-2, JSD-3, SGR 44) were used as working standards for trace elements. In-house standards, made by mixing together a low ash peat with Merck quality oxides or carbonates for each of the major element, were used for the calibration of major elements. The resulting mix was then progressively diluted to obtain five aliquots of different concentrations. Their respective concentrations were previously measured by inductively coupled plasma atomic emission spectrometry (ICP-AES) at the ''Musée Royal d'Afrique Centrale" (MRAC) in Tervuren (Belgium) together with the low ash peat after ashing and acid digestion in a clean laboratory (De Vleeschouwer, 2007). Repeated measurements (n = 20) allowed the estimation of reproducibility and accuracy (Table 1).

Lead isotopes

Twelve samples from CR 1 and five samples from CR 2 (see Table 2 for depths) were prepared in a laminar flow clean air cabinet using the following protocol: 100 mg of peat powder were digested in 30 mL open Savillex Ò beakers (95 °C, 72 h) using successive additions of H 2 O 2 30% p.a. and HNO 3 14 N cc sub in a proportion of 2:1. andCR2) taken aside the road. Wooden structure after [START_REF] Corbiau | Nouvelles recherches archéologiques pluridisciplinaires sur le parcours de la voie médiévale dite la Via Mansuerisca et découverte d'un véhicule dans la Fagne Rasquin à Waimes (Lg)[END_REF]. Vertical scale is exaggerated five times. CR1 is 103 cm long and is located downhill from the road section and CR2 is 125 cm long and is located uphill from the road section.

Samples were then dried, HF 24 N suprapur and HNO 3 14 N cc sub were added in a proportion of 10:1 and the beakers were closed and heated (130 °C, 72 h). After drying, 2 mL of HCl 6.8 N were added and the solutions were slowly evaporated at 75 °C. The dried residues were finally dissolved in 0.5 mL HBr 0.8 N. The Pb separation was achieved by successive HBr and HCl additions on pre-conditioned columns filled with an anionic resin (AG1X8). The eluted pure Pb solution was evaporated and stored. Before isotopic analysis, the Pb elution was re-dissolved in 100 lL of HNO 3 14 N cc sub, evaporated and finally dissolved in 1.5 mL of HNO 3 0.05 N. Lead isotopes were measured using a Nu-plasma multi collector-inductively coupled plasma-mass spectrometer (MC-ICP-MS) at the 'Département des Sciences de la Terre et de l'Environnement' (DSTE -Université Libre de Bruxelles). Results are given in mg/g for major elements and in lg/g for trace elements in dry peat, respectively. Values in italics, underlined and in bold are respectively qualitative (3r-6r), semi-quantitative (6r-9r) and quantitative (>9r). LD, LSQ and LQ mean respectively limit of detection, limit of semiquantification and limit of quantification.

As an internal isotopic standard, a Tl solution was added to each sample and standard to monitor and correct for mass dependent isotopic fractionation. Whilst the samples were characterized by a large variability in Pb concentrations, the sample solutions were prepared to obtain a beam intensity in the Axial collector ( 204 Pb) of a minimum of 100 mV and a Pb/Tl ratio of $5, matching the Pb and Tl concentrations of the NBS981 standard (200 ppb in Pb, with 50 ppb in Tl). The NBS981 standard was measured several times before each analytical session and between each two samples. Forty-one analyses of the standard were performed and gave the following mean values: [START_REF] Weis | High-precision isotopic characterization of USGS reference materials by TIMS and MC-ICP-MS[END_REF]. These values are also in agreement with TIMS triple-spike values previously published by [START_REF] Galer | Practical applications of lead triple spiking correction of instrumental mass discrimination[END_REF]. Although the NBS981 standard results were within the error of the triple-spike values after online correction for instrumental mass bias by Tl addition, the sample results were further corrected by the sample-standard bracketing method (as described by [START_REF] White | High-precision analysis of Pb isotope ratios by multi-collector ICP-MS[END_REF][START_REF] Weis | High-precision isotopic characterization of USGS reference materials by TIMS and MC-ICP-MS[END_REF] to circumvent any instrumental drift during the analytical session. A duplicate (i.e. second sample treated the same way) of CR1 (100-101 cm) and a replicate (i.e. second analysis of the same sample) of CR2 (109-110 cm) were also measured to check the reproducibility (Table 2).

Radiocarbon dating

Six samples of bulk peat powder from CR1 were 14 C-dated. Samples were either 1 cm thick (10-11 cm, 80-81 cm and 82-83 cm), or 2 cm thick, i.e. a mix of two 1 cm-thick samples (74-76 cm, 76-78 cm and 78-80 cm). ''Poz" sam-ples were measured by acceleration mass spectrometry (1.5 SDH-Pelletron Model ''Compact Carbon A.M.S.") at Poznan Radiocarbon Laboratory (Poland) after pre-treatment using an acid-alkali-acid washing sequence in order to remove humic/fulvic acids and bacterial CO 2 [START_REF] Speranza | Improving the time control of the Subboreal/Subatlantic transition in a Czech peat sequence by 14 C wiggle-matching[END_REF]. ''GrN" samples were measured by conventional counting at Center for Isotope Research in Groningen (The Netherlands).

Results

Selected major elements (Si, Al, Na, K)

In both CR1 and CR2, concentrations of Si, Al and K display similar patterns (Table 1). In CR1, concentrations decrease from the base of the section (Si = 148 mg/g, Al = 89 mg/g, Na = 8 mg/g and K = 12 mg/g) to 30 cm (Si = 10.6 mg/g, Al = 16.4 mg/g, Na < DL and K = 0.37 mg/ g) and are low between 30 and 80 cm. Between 80 and 103 cm, concentrations fluctuate from low (Si = 12.4 mg/ g, Al = 24 mg/g, Na = 2.4 mg/g and K = 1.1 mg/g) to high values (Si = 332 mg/g, Al = 102 mg/g, Na = 11 mg/g and K = 13 mg/g). In CR2, elemental concentrations decrease between the bottom sample (Si = 340 mg/g, Al = 250 mg/g and K = 23 mg/g) and 50 cm (Si = 9 mg/g, Al = 2 mg/g and K = 0.14 mg/g). Values are low and stable between 50 cm and 105 cm, then increase towards 122 cm and finally decrease towards the surface. Most of the Na values are below the detection limit in CR2.

Selected contaminant metals

In CR1, Zn and Pb profiles display a similar pattern (Table 1). Between 0 and 70 cm, Zn is below the detection limit while Pb concentrations are low (6 lg/g < Pb < 13.7 lg/g). A significant amount of Zn occurs at 70 cm (49 lg/g) while the Pb content increases to reach 41 lg/g at 70 cm. From 70 cm to 78 cm, concentrations of both elements increase drastically (41 lg/g < Pb < 77 lg/g, 49 lg/g < Zn < 1037 lg/g). Concentrations then decrease towards 81.5 cm (Pb = 10.9 lg/g, Zn = 114 lg/g) and peak twice, at 85.5 cm (Pb = 33 lg/g, Zn = 517 lg/g) and 93.5 cm (Pb = 42 lg/g, Zn = 792 lg/g), respectively. From 98 cm to the surface, the Zn concentration decreases while that of Pb increases strongly. In CR2, Pb concentrations vary between 6.8 and 30.6 lg/g from 0 cm to 110 cm. From 111 cm, Pb values increase and reach around 600 lg/g at 123.5 cm. Zinc is below the detection limit between 10 and 95 cm, except in the bottom sample (5 lg/g). Then

Zn concentrations increase from 111 cm to 123.5 cm to reach 940 lg/g at 123 cm. The Zn profile also displays three peaks at 97.5 cm (20 lg/g), 102.5 cm (53 lg/g) and 109.5 cm (76 lg/g), respectively.

Lead isotopes

Table 2 summarises results of Pb isotope analyses. In CR1 (Table 2), 208 Pb/ 204 Pb, 207 Pb/ 204 Pb and 206 Pb/ 204 Pb isotopic ratios decrease from the bottom (respectively, 38.9589 ± 0.0153, 15.7012 ± 0.0057 and 19.1661 ± 0.0071) to 70.5 cm (respectively, 38.3883 ± 0.0149, 15.6268 ± 0.0057 and 18.3984 ± 0.0072). From 70.5 cm to 98.5 cm values are stable (respectively, between 38.3120 ± 0.0106 and 38.3991 ± 0.0177, between 15.6236 ± 0.0041 and 15.6288 ± 0.0068 and between ± 0.0053 and 18.4255 ± 0.0067) except in sample 81.5 cm which displays higher values (respectively, 38.6681 ± 0.0208, 15.6603 ± 0.0079 and 18.7404 ± 0.0081). The sample located near the surface presents the lowest values (respectively, 38.1746 ± 0.0169, 15.6117 ± 0.0067 and 18.1879 ± 0.0079).

In CR2, 208 Pb/ 204 Pb, 207 Pb/ 204 Pb and 206 Pb/ 204 Pb isotopic ratios decrease from 50 cm (respectively, 38.8087 ± 0.0113, 15.6872 ± 0.0036 and 19.0550 ± 0.0043) towards the surface (38.0000 ± 0.0098, 15.5952 ± 0.0039 and 18.0354 ± 0.0053).

Radiocarbon dates

Results were calibrated using Oxcal 3.10 (Bronk Ramsey, 2001) and four selected dates (74-76, 76-78, 78-80 and 80-81 cm) were wiggle-matched using a Bayesian approach developed for peat in the calibration tool Bpeat [START_REF] Blaauw | Radiocarbon peat chronologies and environmental change[END_REF]. The data set is coherent even if intervals are partly overlapping in the Bpeat-calibrated samples (Table 3). This overlap is due to (1) the continuity of sampling for 14 C dating and (2) the high compaction of the peat making a 1 cm-thick slice to represent several tens of years. Therefore, there is an overlap which is however chronologically ordered. For example, sample GrN29296 (74-76 cm) displays the oldest probablility age of AD 19 and the youngest probability of AD 200. The directly above sample GrN29297 (76-78 cm height) displays the oldest probablility age of AD 86 (i.e. younger than AD 19) and the youngest probability of AD 214 (i.e. younger than AD 200). The same goes between GrN29297 (76-78 cm height) and GrN29298 (78-80 cm height), and between GrN29298 (78-80 cm height) and Poz11378 (80-81 cm height). Bcal Bayesian approach [START_REF] Buck | The Bayesian Approach to Interpreting Archaeological Data[END_REF] was also tested (results not reported here) but did not improve the results from Bpeat. Calibration using Bpeat provided smaller intervals. In the following discussion, these Bpeat-calibrated age dates will therefore be used together with the Oxcal-calibrated age dates of the two other samples.

Discussion

Environmental impact

Building and use of the road

Geochemical analyses provide clear documentation not only about the impact of the road on the surrounding environment, but also about one of its possible purposes, namely ore transport. Sudden increases in Si concentrations in both peat columns show a direct impact of the building and the regular use of the road. The first significant Si concentrations occur at 81.5 and 106.5 cm height, respectively in CR1 and CR2 (Fig. 3). The Al, Na and K profiles also follow the same trend. Careful observation of thin sections from these depth intervals reveals a strong contamination of the peat by numerous Revinian quartzite particles used to cobble the road. This material is therefore assumed to have been produced during the construction and the use of the road. Absolute concentration discrepancies are explained by the water stream causing preferential The calibrated age intervals in bold are used in the discussion. accumulation to the eastern side of the road. The sample below (80.5 cm) and the sample above (82.5 cm) the Si peak were respectively dated at AD 152-328 and AD 350-540 (Fig. 4). The youngest date indicates that the road was already cobbled before AD 350-540. The oldest date must be interpreted cautiously due to the random mode of particle deposition and the lack of information about the time span between the cobbling and the first particle accumulation. However, it seems reasonable to assume that this accumulation started as soon as the cobbling was realized, i.e. during or after AD 152-328. Higher Pb and Zn concentrations suggest a strong local pollution possibly beginning between AD 19 and AD 120 and peaking between AD 86 and AD 328. (Fig. 4). Particular levels (between 81 cm and 84 cm, and between 86 cm and 88 cm height, respectively) display low Zn and Pb content due to the important amount of quartzite fragments, increasing the Si signal and diluting the Pb and Zn concentrations. In Belgium, Pb and Zn concentrations have been previously measured in a core from a nearby ombrotrophic peat bog (De Vleeschouwer et al., 2007). This record displays quite similar Pb concentrations (40 lg/ g < Pb < 100 lg/g) during the same time span, possibly reflecting the Pb pollution found here. However, Zn concentrations are often very low (8 lg/g < Zn < 35 lg/g) or below the detection limit, excepted in AD 1950 210 Pb-dated peat layers where Zn peaks at 250 lg/g. This value is still 4 times less than the one found beside the cobbled road. A study carried out by [START_REF] Kempter | Der Verlauf des anthropogenen elementeintrags in Regenwassermoore des westlichen Mitteleuropas während des jüngeren Holozäns[END_REF] in another nearby ombrotrophic bog showed no particular enrichment in Zn or Pb during the first five centuries AD. It can therefore be concluded that the peat aside the cobbled road has recorded a very local Pb and Zn pollution. Such pollution is likely to be from the transport of Pb-Zn-rich material on the road.

Sources of pollution

Lead isotopes are used to discriminate between possible Pb sources, especially at the highly Pb-Zn-polluted levels. Lead isotopic data define two trend lines (Fig. 5). The right (i.e. higher 206 Pb/ 207 Pb and lower 208 Pb/ 206 Pb ratios) trendline is defined by the Verviers Pb-Zn ores [START_REF] Pasteels | La composition isotopique du plomb des gisements belges. Implications sur les plans génétique et économique. (Note préliminaire)[END_REF][START_REF] Cauet | Genetic study of Belgian lead and zinc mineralizations in carbonate environments through lead isotopic geochemistry[END_REF][START_REF] Dejonghe | Zinc-lead deposits of Belgium[END_REF] and a crustal (i.e. non anthropogenic) source. This crustal source differs significantly from the mean upper continental crust values defined by several authors [START_REF] Asmerom | The Pb isotopic evolution of the earth: inferences from river water suspended loads[END_REF][START_REF] Hemming | Pb isotope compositions of modern deep sea turbidites[END_REF][START_REF] Millot | Lead isotopic systematics of major river sediments: a new estimate of the Pb isotopic composition of the Upper Continental Crust[END_REF]. It fits rather better with the Belgian pre-industrial background values proposed by [START_REF] Sonke | A chemical and mineralogical reconstruction of Zn smelter emissions in the Kempen region (Belgium), based on organic pool sediment cores[END_REF] and De Vleeschouwer et al. (2007). The left trendline is defined by the Verviers Pb-Zn ores and the recent (1994)(1995)(1996)(1997)(1998)(1999) urban aerosols from nearby Germany and The Netherlands [START_REF] Bollhöfer | Isotopic source signatures for atmospheric lead: the northern hemisphere[END_REF].

In section CR1, samples from the lower part of the peat column (9.5 cm and 40.5 cm) show that the main inorganic inputs to these layers derive from the regional soil and rock erosion as their isotopic signatures are in good agreement with the Belgian pre-industrial background. Samples situated in the highly Zn-and Pb-contaminated interval (i.e. 60-99 cm, n = 8) are all centred upon the isotopic field of the Pb-Zn ores of the Verviers syncline, located 15 km northwards of the excavation site. This observation is in good agreement with the hypothesis that this road was used for ore transport. The sample from 81.5 cm shows a lower 208 Pb/ 206 Pb ratio and a higher 206 Pb/ 207 Pb ratio that can be explained by the occurrence of quartzite fragments (with a crustal Pb isotopic signature). The uppermost peat sample (100.5 cm) displays a signature in good agreement with modern aerosols.

Samples from CR2 display the same trend. Samples at 50.5 cm and 96.5 cm height show isotopic ratios similar to the Belgian pre-industrial background. Samples at 102.5 cm and 109.5 cm (i.e. samples with Pb-Zn contamination) display Pb isotopic ratios in good agreement with the Verviers Pb-Zn ores field. This again favours the hypothesis of ore transport on the road. The uppermost (i.e. recent) sample shows Pb isotopic ratios similar to modern aerosols.

Post-depositional mobility of contaminant metals

The archaeological findings presented here are for the area located down slope on a peatland where surface runoff was observed during the sampling. Punctual inorganic inputs are thus likely. The question of whether these phenomena could affect the geochemistry of the peat must therefore be assessed.

Investigations of pollution history in peat are usually achieved in ombrotophic bogs, (e.g. [START_REF] West | Heavy metals in Holocene peats from South West England: detecting mining impacts and atmospheric pollution[END_REF][START_REF] Shotyk | History of atmospheric lead deposition since 12,370 14 C yr BP from a peat bog, Jura mountains[END_REF][START_REF] Martínez-Cortizas | Four thousand years of atmospheric Pb, Cd and Zn deposition recorded by the ombrotrophic peat bog of Penido Vello (Northwestern Spain)[END_REF][START_REF] Shotyk | The chronology of anthropogenic, atmospheric Pb deposition recorded by peat cores in three minerogenic peat deposits from Switzerland[END_REF][START_REF] Nieminen | Enrichments of Cu, Ni, Zn, Pb and As in an ombrotrophic peat bog near a Cu-Ni smelter in Southwest Finland[END_REF][START_REF] Mighall | Geochemical evidence for atmospheric pollution derived from prehistoric copper mining at Copa Hill, Cwmywtwyth, mid-Wales[END_REF]Le Roux et al., 2004a;De Vleeschouwer et al., 2007). However, a few studies have demonstrated the potential of minerotrophic peat to record past geochemical changes, either natural or anthropogenic, (e.g. [START_REF] West | Heavy metals in Holocene peats from South West England: detecting mining impacts and atmospheric pollution[END_REF][START_REF] Shotyk | The chronology of anthropogenic, atmospheric Pb deposition recorded by peat cores in three minerogenic peat deposits from Switzerland[END_REF][START_REF] Baron | Record of metal workshops in peat deposits: history and environmental impact on the Mont Lozère Massif[END_REF]. In addition, the knowledge of local pol-lution sources is of high interest to accurately reconstruct global contaminant metal pollution [START_REF] Baron | Record of metal workshops in peat deposits: history and environmental impact on the Mont Lozère Massif[END_REF]. Lead has been used as an atmospheric pollution tracer in several geochemical studies in peat bogs, (e.g. [START_REF] Martínez-Cortizas | Four thousand years of atmospheric Pb, Cd and Zn deposition recorded by the ombrotrophic peat bog of Penido Vello (Northwestern Spain)[END_REF][START_REF] Shotyk | History of atmospheric lead deposition since 12,370 14 C yr BP from a peat bog, Jura mountains[END_REF][START_REF] Mighall | Geochemical evidence for atmospheric pollution derived from prehistoric copper mining at Copa Hill, Cwmywtwyth, mid-Wales[END_REF]. Most authors have considered Pb as being immobile in ombrotrophic peat [START_REF] Shotyk | History of atmospheric lead deposition since 12,370 14 C yr BP from a peat bog, Jura mountains[END_REF][START_REF] Shotyk | A new approach for quantifying cumulative, anthropogenic, atmospheric lead deposition using peat cores from bogs: Pb in eight Swiss peat bog profiles[END_REF][START_REF] Mighall | Geochemical evidence for atmospheric pollution derived from prehistoric copper mining at Copa Hill, Cwmywtwyth, mid-Wales[END_REF][START_REF] Martínez-Cortizas | Four thousand years of atmospheric Pb, Cd and Zn deposition recorded by the ombrotrophic peat bog of Penido Vello (Northwestern Spain)[END_REF][START_REF] Jones | Ombrotrophic peat as a medium for historical monitoring of heavy metal pollution[END_REF] and in some cases also in minerotrophic peat [START_REF] Shotyk | The chronology of anthropogenic, atmospheric Pb deposition recorded by peat cores in three minerogenic peat deposits from Switzerland[END_REF]. Elevated amounts of Pb were therefore considered as contemporaneous of the level that records it.

Zinc mobility in peat is however still under debate. Its distribution is linked, among others, to bioaccumulation, water table fluctuation and pH conditions [START_REF] Shotyk | Review of the inorganic geochemistry of peats and peatland waters[END_REF]. Zinc distribution can also be linked to the type of vegetation as different parts of the same plant can concentrate Zn in different ways [START_REF] Livett | Lead, zinc and copper analysis of British blanket peats[END_REF]. Zinc seems to be more mobile than Pb and therefore more likely to be leached [START_REF] Livett | Lead, zinc and copper analysis of British blanket peats[END_REF]. Recently, [START_REF] Weiss | Atmospheric deposition and isotope biogeochemistry of zinc in ombrotrophic peat[END_REF] have demonstrated Zn mobility in peat cores from Finnish natural and polluted sites. They suggest that Zn is affected by multiple biogeochemical processes. They therefore recommand that these processes have to be taken into account before using Zn as a tracer of pollution. However, even more recently, [START_REF] Sonke | Historical variations in the isotopic composition of atmospheric zinc deposition from a zinc smelter[END_REF] have found deep Zn and Pb peaks in organic sediment from Belgium. They correlate these peaks with the well known history of local Zn and Pb smelting. They concluded, conversely to [START_REF] Weiss | Atmospheric deposition and isotope biogeochemistry of zinc in ombrotrophic peat[END_REF] that Zn is not subject to vertical migration. [START_REF] Bollhöfer | Isotopic source signatures for atmospheric lead: the northern hemisphere[END_REF]. Light grey field (18 points) represents the nearby (less than 10 km) Pb-Zn ores from the Verviers syncline [START_REF] Cauet | Genetic study of Belgian lead and zinc mineralizations in carbonate environments through lead isotopic geochemistry[END_REF][START_REF] Dejonghe | Zinc-lead deposits of Belgium[END_REF]. Dark grey field (4 points) represents the Upper Continental Crust [START_REF] Millot | Lead isotopic systematics of major river sediments: a new estimate of the Pb isotopic composition of the Upper Continental Crust[END_REF][START_REF] Hemming | Pb isotope compositions of modern deep sea turbidites[END_REF][START_REF] Grousset | Transient Pb isotopic signatures in the western-European atmosphere[END_REF][START_REF] Asmerom | The Pb isotopic evolution of the earth: inferences from river water suspended loads[END_REF]. Oblique dashed area represents the Belgian pre-industrial background proposed by [START_REF] Sonke | A chemical and mineralogical reconstruction of Zn smelter emissions in the Kempen region (Belgium), based on organic pool sediment cores[END_REF]. White stars are the local pre-industrial background in Belgian peat proposed by De Vleeschouwer et al. (2007).

Despite this debate, Zn is regularly used to trace pollution history linked to mining activities, but explanations depend on the context. [START_REF] Mighall | Geochemical evidence for atmospheric pollution derived from prehistoric copper mining at Copa Hill, Cwmywtwyth, mid-Wales[END_REF] studied pollution history linked to the Pb-Zn ore mining in a blanket peat. In their study, Pb concentrations were in good agreement with the mining activities history. Zinc concentrations could therefore also reflect mining activities. However, the authors suggested caution as the data showed possible re-mobilization which may have blured the actual boundaries of deposition. [START_REF] West | Heavy metals in Holocene peats from South West England: detecting mining impacts and atmospheric pollution[END_REF] studied the pollution history linked to the mining of various (including Pb and Zn) ores. Concentration patterns and enrichment factors were interpreted as reflecting the regional pollution but elemental mobility was not discussed. [START_REF] Jones | Ombrotrophic peat as a medium for historical monitoring of heavy metal pollution[END_REF] measured major and trace element concentrations in peat. The resulting statistical treatment showed that Zn and Pb were strongly correlated. They showed the same pattern, most likely indicating anthropogenic impact, and were at their initial level of deposition. In this peat bog, Zn was not mobilized. From this brief overview, it could be concluded that Pb is the best indicator and that Zn can be a good second element to trace past pollution.

In the peat columns studied here, post-depositional mobilization of Pb and Zn is unlikely. Indeed, samples with high Zn and Pb content (CR1 between 60 and 99 cm excluding the 80.5 cm sample) fit within a narrow range of Pb isotopic ratios (Fig. 5). Moreover, all these ratios fall within the field of Verviers syncline Pb-Zn ores. If any mobilization of Pb from samples above the first Si peak had occurred, a progressive decrease of Pb and Zn content down-core would have been expected, together with a mixed Pb isotopic signature between Verviers ores and Belgian pre-industrial background. This is clearly not observed here. The stability of Pb isotopic ratios has already been used by [START_REF] Baron | Record of metal workshops in peat deposits: history and environmental impact on the Mont Lozère Massif[END_REF] as an argument to attest to Pb immobility in fen (i.e. minerotrophic) peat in France. Moreover, Pb and Zn display a high degree of correlation (R 2 = 0.88) in CR1 between 76 and 94 cm. This suggests a common origin and deposition process for Pb and Zn. It also favours the immobility of both elements.

Early mining activities and purpose of the road

In conjunction with more conventional road uses, e.g. civilian and military movement, trade routes, etc. geochemical investigations carried out here provide clear evidence for the road being used for the transport of local Pb and Zn ores from the Verviers syncline. These ores are known to have been mined from the 14th century [START_REF] Dejonghe | Atlas des gisements plombo-zincifères du synclinorium de Verviers (Est de la Belgique)[END_REF]. Although the extraction of Pb-Zn ores of the Verviers syncline during Roman or even Celtic times is mentioned in the literature [START_REF] Dejonghe | Zinc-lead deposits of Belgium[END_REF][START_REF] Ladeuze | La Vieille-Montagne, l'exploitation minière et la métallurgie du zinc dans l'ancien duché de Limbourg[END_REF], it only refers to [START_REF] Plini | Histoires Naturelles[END_REF] who vaguely mentioned that an ore called Cadmia was extracted in ''Germania". No more precise location was mentioned. In addition, there is no archaeological, palynological or geochemical evidence attesting to an early mining of Pb and Zn or smelting activities in East Belgium. However, various archaeological artefacts found in and around the Hautes Fagnes area (Gilot, 1977; Dumont, 1979, 1980; Fig. 6. 208 Pb/ 206 Pb vs. 206 Pb/ 207 Pb isotopic biplot showing data from CR1 (black circles) and CR2 (white diamonds) compared to isotopic signatures of Verviers Pb-Zn ores (grey shaded area), German Eifel Pb ores (dashed line areas, after [START_REF] Durali-Mueller | Roman lead mining in Germany: its origin and development through time deduced from lead isotope provenance studies[END_REF] and German Pb artefacts (enclosed symbols) from various locations (after [START_REF] Durali-Mueller | Roman lead mining in Germany: its origin and development through time deduced from lead isotope provenance studies[END_REF]. The error ranges are smaller than the symbols. [START_REF] Remy | Monographie archéologique Commune de Vielsalm[END_REF][START_REF] Cauuet | Les mines d'or antiques d'Europe hors péninsule Ibérique. État des connaissances et travaux récents[END_REF], like alluvial mounds remaining from Au prospecting (ranging from BC 120 -AD 140 to BC 400-200), graves, coins and remains of cities and villages, attest to an early occupation. The increasing anthropogenic impact of local population is also recorded by increases in Plantago lanceolata and cereal pollen in dated peat cores [START_REF] Damblon | Les dépôts tourbeux et l'histoire de la végétation sur le plateau des Hautes Fagnes (Belgique)[END_REF][START_REF] Gotjé | A palynological study of a Holocene deposit from Grand Bongard (Hautes Fagnes, Belgium)[END_REF].

The dataset presented here, especially the strong Pb isotopic similarity between contaminated peat layers and local ores, may therefore represent the first evidence for ore mining during early Roman to Merovingian times. Together with the high elemental concentrations in Pb and Zn, it can also be assumed that these ores were transported on the road across the Hautes Fagnes.

As mentioned in Section 1, Trier has already been considered to be the destination of the road. This city is known to have been a Late Roman capital, a major centre of coinage [START_REF] Sutherland | Diocletian to Maximinus. Roman Imperial Coinage[END_REF], a key crossroad and a fluvial point. Numerous Pb artefacts have been found in archaeological excavations in this area. Several of them have been investigated for their Pb isotopic ratios by [START_REF] Durali-Mueller | Roman lead mining in Germany: its origin and development through time deduced from lead isotope provenance studies[END_REF], together with artefacts from other nearby locations (Mainz, Wallendorf, Martberg) west to the Rhine river. Lead isotopic signatures of these artefacts correspond to the signatures of German Pb ores. However, Pb isotopic ra-tios of these artefacts also show an important overlap with the data presented here and with the isotopic signatures of Verviers Pb-Zn ores (Fig. 6). As strong Pb-Zn pollution is encountered in the peat near the road during late Roman times, Belgian Pb-Zn ores must have therefore been mined and transported towards Germany and may also have used in the fabrication of various Pb objects in the Trier area. Moreover, several Cu ore deposits were also found around this city (Fig. 7). Romans are known to have made some of their coins and other objects with brass [START_REF] Halleux | La fabrication du laiton[END_REF], which is a Zn-Cu alloy. Assembling all this information, it seems legitimate to propose that Zn and Pb ores were mined in the Verviers syncline and transported through the Hautes Fagnes towards Trier.

As Pb and Zn peaks are considered to reflect ore transport, the time interval of AD 86-328 provides a minimum age-date for this transport and its impact on the peat. It fits clearly within Roman times (see Fig. 4) and is in good agreement with the suggestion developed above. However, the road was probably not cobbled before AD 152-328 (see Section 5.1.1). Such a discrepancy between ore transport (attested by the first Pb-Zn contamination) and the cobbling (attested by the first Si contamination) may be due either to the random quartzite deposition mode, or to an effective ore transport on an early non-cobbled road. How- Corbiau, 1981b and[START_REF] Permingeat | Carte des gîtes minéraux[END_REF]. ever, due to the large overlap between each age interval, the present data do not allow distinguishing between the two hypotheses. Archaeological investigations are still ongoing and might provide additional support for the chronology of the road construction.

Conclusions

The geochemical investigation of peat columns collected alongside an ancient cobbled road in SE-Belgium documents the road's impact on the local environment but also provides new perspectives for future geoarchaeological research in general.

At a local scale, the investigation shows that: (1) high contents of Si, Al, Na and K reflect early peat pollution when cobbles and finer material were eroded during the building and use of the road; (2) the precise date of the road cobbling is still unclear. However, the occurrence of mineral particles in the peat evidence the presence of the cobbled road just before AD 350-540 and probably not before AD 152-328; (3) the mineral pollution is also preceded by a Pb-Zn pollution. Lead isotopic ratios reveal that the road served, among other things, to transport Pb-Zn ores from nearby Verviers Pb-Zn ore deposits.

It is therefore concluded that the onset of ore transport started during the early Roman times. This time frame is in good agreement with other archaeological evidence of Roman activities in the area. Geochemical findings from this study also support that the Belgian Pb-Zn ores from Verviers syncline could have been mined as early as during early Roman times. It is therefore suggested that in similar studies, the local isotopic source should be taken into consideration when dealing with past pollution reconstruction for this time period.

More generally, Zn is apparently immobile in the profiles, due to its similar behaviour to Pb. Moreover, the preservation of an ancient road and its environmental impact in a peatland also provides the unique opportunity to directly trace palaeopollution close to an archaeological site using geochemistry. More interest should be taken on similar ancient roads or other archaeological sites, in terms of their possible impact on the immediate environment.

This study demonstrates how geochemistry can be successfully applied to an archaeological problem. Geochemistry can indeed be used as a tool to investigate small scale changes in peat columns and to provide conclusion in terms of ore mining, routes and trade, and therefore to give insights to solve historical problems.

Fig. 1 .

 1 Fig. 1. (A) Location map of the Hautes Fagnes plateau, the Pb-Zn ores of E-Belgium[START_REF] Cauet | Genetic study of Belgian lead and zinc mineralizations in carbonate environments through lead isotopic geochemistry[END_REF][START_REF] Dejonghe | Zinc-lead deposits of Belgium[END_REF], the cobbled road and the various excavations (afterCorbiau, 1981a). Peat thickness reported from[START_REF] Wastiaux | Topographie de surface et de subsurface des zones tourbeuses des réserves naturelles domaniales des Hautes Fagnes[END_REF]. (B) Sketch of the findings from[START_REF] Bastin | La Via Mansuerisca[END_REF] redrawn by[START_REF] Mertens | Les routes romaines de la Belgique[END_REF].

Fig. 2 .

 2 Fig. 2. (A) Picture of the excavation in course of study. The position of CR1 is shown. (B) Schematic drawing of the two peat sections (CR1 and CR2) taken aside the road. Wooden structure after[START_REF] Corbiau | Nouvelles recherches archéologiques pluridisciplinaires sur le parcours de la voie médiévale dite la Via Mansuerisca et découverte d'un véhicule dans la Fagne Rasquin à Waimes (Lg)[END_REF]. Vertical scale is exaggerated five times. CR1 is 103 cm long and is located downhill from the road section and CR2 is 125 cm long and is located uphill from the road section.

Fig. 3 .

 3 Fig. 3. Selected elemental concentrations (major + trace elements) in CR1 and CR2. Lithological information is based on microscopic observation on thin sections.

Fig. 4 .

 4 Fig. 4. The 14 C based chronology performed on the CR1 profile (see text for details).

Fig. 5 .

 5 Fig.5.208 Pb/ 206 Pb vs.206 Pb/ 207 Pb isotopic biplot. Black dots and white diamonds are samples from CR1 and CR2, respectively. The error ranges are smaller than the symbols. Horizontal dashed field encompasses samples of CR1 between 60-99 cm height (i.e. eight samples with very high Zn and high Pb contents). White field (13 points) represents the modern aerosols from Belgium, nearby Germany and The Netherlands[START_REF] Bollhöfer | Isotopic source signatures for atmospheric lead: the northern hemisphere[END_REF]. Light grey field (18 points) represents the nearby (less than 10 km) Pb-Zn ores from the Verviers syncline[START_REF] Cauet | Genetic study of Belgian lead and zinc mineralizations in carbonate environments through lead isotopic geochemistry[END_REF][START_REF] Dejonghe | Zinc-lead deposits of Belgium[END_REF]. Dark grey field (4 points) represents the Upper Continental Crust[START_REF] Millot | Lead isotopic systematics of major river sediments: a new estimate of the Pb isotopic composition of the Upper Continental Crust[END_REF][START_REF] Hemming | Pb isotope compositions of modern deep sea turbidites[END_REF][START_REF] Grousset | Transient Pb isotopic signatures in the western-European atmosphere[END_REF][START_REF] Asmerom | The Pb isotopic evolution of the earth: inferences from river water suspended loads[END_REF]. Oblique dashed area represents the Belgian pre-industrial background proposed by[START_REF] Sonke | A chemical and mineralogical reconstruction of Zn smelter emissions in the Kempen region (Belgium), based on organic pool sediment cores[END_REF]. White stars are the local pre-industrial background in Belgian peat proposed byDe Vleeschouwer et al. (2007).

Fig. 7 .

 7 Fig.7. The cobbled road in the historical and geographical context. Principal Cu, Zn and Pb ores are also reported. (modified afterCorbiau, 1981b and[START_REF] Permingeat | Carte des gîtes minéraux[END_REF].

Table 1

 1 Selected elemental geochemistry in CR1 and CR2 cores

	CR1

Table 2

 2 Pb-isotopic ratios in selected samples from CR1 and CR2

	Height (cm)	208 Pb/ 204 Pb	2sd	207 Pb/ 204 Pb	2sd	206 Pb/ 204 Pb	2sd	208 Pb/ 206 Pb	2sd	207 Pb/ 206 Pb	2sd
	CR1
	100.5 *	38.1746	0.0169	15.6117	0.0067	18.1879	0.0079	2.09887	0.00037	0.85830	0.00012
	100.5	38.1807	0.0154	15.6139	0.0057	18.1916	0.0064	2.09874	0.00045	0.85825	0.00013
	98.5	38.3991	0.0177	15.6288	0.0068	18.4255	0.0067	2.08402	0.00036	0.84815	0.00011
	93.5	38.3355	0.0178	15.6260	0.0062	18.3709	0.0067	2.08673	0.00037	0.85053	0.00010
	85.5	38.3457	0.0152	15.6279	0.0061	18.3682	0.0066	2.08764	0.00044	0.85076	0.00012
	81.5	38.6681	0.0208	15.6603	0.0079	18.7404	0.0081	2.06340	0.00004	0.83561	0.00012
	80.5	38.3528	0.0160	15.6248	0.0058	18.3868	0.0060	2.08591	0.00038	0.84974	0.00011
	77.5	38.3120	0.0106	15.6236	0.0041	18.3299	0.0053	2.09010	0.00029	0.85230	0.00008
	75.5	38.3506	0.0169	15.6252	0.0061	18.3657	0.0074	2.08813	0.00045	0.85073	0.00011
	70.5	38.3883	0.0149	15.6268	0.0057	18.3984	0.0072	2.08641	0.00035	0.84928	0.00011
	60.5	38.4817	0.0180	15.6387	0.0067	18.4532	0.0072	2.08542	0.00034	0.84744	0.00011
	40.5	38.7448	0.0290	15.6745	0.0079	18.8368	0.0181	2.05707	0.00072	0.83216	0.00017
	9.5	38.9589	0.0153	15.7012	0.0057	19.1661	0.0071	2.03270	0.00038	0.81917	0.00011
	CR2
	123.5 109.5 **	38.0000 38.3886	0.0098 0.0105	15.5952 15.6212	0.0039 0.0038	18.0354 18.4096	0.0053 0.0035	2.10686 2.08510	0.00020 0.00022	0.86468 0.84852	0.00006 0.00005
	109.5	38.3879	0.0126	15.6212	0.0053	18.4111	0.0049	2.08495	0.00020	0.84848	0.00007
	102.5	38.4798	0.0084	15.6297	0.0032	18.4918	0.0053	2.08085	0.00023	0.84521	0.00008
	96.5	38.6165	0.0124	15.6488	0.0042	18.6344	0.0049	2.07228	0.00021	0.83979	0.00007
	50.5	38.8087	0.0113	15.6872	0.0036	19.0550	0.0043	2.03662	0.00027	0.82325	0.00007

''sd" refers to standard deviation. Duplicate is denoted by * while replicate is denoted by ** .

Table 3

 3 The 14 C dates on 6 samples from CR1. Three samples (74-76 cm, 76-78 cm and 78-80 cm height) are a mix of two 1 cm-thick slices

	Height	14 C	Uncertainty Calibrated ages Oxcal (Bronk Ramsey, 2001)	Calibrated ages Bpeat wiggle-matching (Blaauw and	Lab no.
	(cm)	date		version 3.10 (2005)	Christen, 2005)
	82-83	1625	30	AD 350-540	-	Poz-
						11552
	80-81	1765	30	AD 130-380	AD 152-328	Poz-
						11378
	78-80	1810	60	AD 70-380	AD 131-258	GrN-
						29298
	76-78	1860	50	AD 50-320	AD 86-214	GrN-
						29297
	74-76	1930	40	BC 40-AD 210	AD 19-200	GrN-
						29296
	10-11	4580	50	BC 3510-3090	-	GrN-
						29473

Acknowledgements

We warmly thank Marie-Hélène Corbiau (Direction de l'Archéologie du Ministère de la Région Wallonne) for providing an easy access to the archaeological site. We are grateful to Guy Bologne and Sophie Leclercq for the XRF analyses, J-P Cullus and F. Boulvain for thin section preparation, and to Maarten Blaauw (Queen's University, Belfast) for his fruitful comments on the age-dating. This manuscript benefited from constructive reviews by Tim Mighall and Gaël Le Roux. We thank Ron Fuge for the editorial handling of the manuscript, Philippe Claeys (Vrije Universiteit Brus-sel) for comments on an earlier version of this manuscript and Maria Gehrels (Univ. Plymouth, UK) for the English smoothing. This work was funded by NSRF (Belgian Scientific Research Foundation) credits. Additional funds (for dating) were provided by the ASBL Parc Naturel Hautes Fagnes-Eifel and the Ministère de la Région Wallonne. François De Vleeschouwer was supported by a FRIA fellowship.


Astrid Casadei

Pierre Ramet

Jean Roman

Nested dissection with balanced halo

come

Nested has been introduced by A. George in 1973 ([4]) and is now a well-known and very popular heuristic for sparse matrix ordering to reduce both the fill-in and the operation count during the numerical factorization. The basic standard idea is to build a "small separator C" associated with the original matrix in order to split the remaining vertices in two parts A and B of "almost equal size". The vertices of the separator C are ordered with the largest indices, and then the same method is applied recursively on the two subgraphs induced by A and B. This method has been implemented by graph partitioners such as METIS or SCOTCH whose main objectives are to minimize the size of the separator and to equilibrate the size of the two separated subgraphs. However, if we examine precisely the complexity analysis for the estimation of asymptotic bounds for fill-in or operation count when using Nested Dissection ordering, we can notice that the size of the halo of the separated subgraphs (set of external vertices adjacent to the subgraphs and previously ordered) play a crucial role in the asymptotic behavior achieved.

Moreover, this method based on a divide and conquer approach is also very well suited to maximize the number of independent computation tasks for parallel implementations. Then, by using the block data structure induced by the partition of separators of the original graph, very efficient parallel block solvers have been designed and implemented according to supernodal or multifrontal approaches. To name a few, one can cite MUMPS, PaStiX and SuperLU. Considering now hybrid methods mixing both direct and iterative solvers such as HIPS [START_REF] Gaidamour | A parallel direct/iterative solver based on a Schur complement approach[END_REF], MaPHYS [START_REF] Agullo | Parallel algebraic domain decomposition solver for the solution of augmented systems[END_REF][START_REF] Giraud | Sparse approximations of the Schur complement for parallel algebraic hybrid linear solvers in 3D[END_REF], PDSLIN [START_REF] Yamazaki | On techniques to improve robustness and scalability of a parallel hybrid linear solver[END_REF] and ShyLU [START_REF] Rajamanickam | ShyLU: A hybrid-hybrid solver for multicore platforms[END_REF], obtaining a domain decomposition leading to a good balancing of both the size of domain interiors and the size of interfaces is a key point for load balancing and effciency in a parallel context.

For this purpose, we revisit the algorithm introduced by Lipton, Rose and Tarjan ( [START_REF] Lipton | Generalized nested dissection[END_REF]) in 1977 which performed the recursion in a different manner: at each level, we apply recursively the method to the subgraphs induced by A ∪ C on one hand, and B ∪ C on the other hand. In these subgraphs, vertices already ordered (and belonging to the previous separators) are the halo vertices and the partition of these overlapping subgraphs is performed with three objectives: balancing of the two new parts A ′ and B ′ , balancing of the halo vertices in the parts A ′ and B ′ and minimizing the size of the separator C ′ .

Our work is implemented in the Scotch partitioner [START_REF] Pellegrini | Scotch: A software package for static mapping by dual recursive bipartitioning of process and architecture graphs[END_REF]. By default, Scotch strategy to find a separator is based on the multilevel method [START_REF] Hendrickson | A multi-level algorithm for partitioning graphs[END_REF][START_REF] Karypis | A fast and high quality multilevel scheme for partitioning irregular graphs[END_REF]: the (sub-)graph is coarsened multiple times until it becomes small enough, then an algorithm called greedy graph growing is applied on the coarsest graph to partition it, and finally the graph is uncoarsened, projecting the coarse separator on finer graph and refining it using the Fiduccia-Mattheyses algorithm [START_REF] Fiduccia | A linear-time heuristic for improving network partitions[END_REF].

We have adapted the multilevel framework of Scotch in order to take into account the halo vertices from orginal to coarsest graph. Moreover, we have worked on two variants of greedy graph growing. The first one is called double greedy graph growing. Its principle is to pick two seed vertices as far as possible among the halo, and to make parts A and B grow from them, with attention paid to keep halo balanced among the growing parts. The second approach, called halo-first greedy graph growing, works in a first stage on the sole halo graph, finding a separator of it. Once it is done, it defines the two halo parts A h and B h as two sets of seeds and make these sets grow in the whole graph to build A and B. Finally, we have also changed the Fiduccia-Mattheyses refinement algorithm in order to preserve the good balancing in the finer graphs. Our algorithms will be explained more deeply during the presentation, with detailed results.

In addition to this algorithmic work, and especially for the MaPHYS solver, a complexity analysis is currently carried on regarding the good asymptotic size for the subdomains (in which a sparse direct factorization is performed) in order to have the same asymptotic complexity bound for the computation of the preconditioner and for the iterative part. This is done by using the same theoretical framework used in [START_REF] Lipton | Generalized nested dissection[END_REF] for general families of graph associated with 3D irregular problems for elliptic PDEs where the maximum number of iterations depends of the number of subdomains. The result is achieved by using balancing properties for the domain interior sizes and for the halo sizes as expected in the first work presented above.


George Barbu
email: barbu@uic.org.

Juliette Marais

The SATLOC project

Keywords: Railway, GNSS, EGNOS. Résumé Application ferroviaire, GNSS, EGNOS

Successful introduction of the satellite navigation technology in the railway safety needs accreditation of a new mode of thinking, innovation, convincing demonstration of concept and lifting of technical and mentality barriers."

This article shows a the state of the art of the SATLOC project aiming at reporting on the baseline of the project according to the objectives, in line with the terms of the FP7, item Galileo.2011.1.4-1 "Use of EGNOS and GALILEO for safety-of-life applications for all transport modes". The article summarizes the notable realizations of the project team, the advanced start of tests, preceded by the concept validation in the laboratory and on the pilot line Brasov-Zarnesti in Romania.

SATLOC and its background

Since the beginning of the years 2000 a number of EC projects (APOLO, GADEROS and LOCOPROL) have tested the GNSS technology on-board of trains and have positively concluded on the capability of GNSS to satisfy the requirements of the railway applications.

The SATLOC (Satellite based operation and management of local low traffic lines) project comes within the scope of this long-term work. Its objective is to develop and demonstrate an innovative concept of applying the GNSS to railway safety and advanced operation on low traffic lines aiming at:

• Stimulate adoption of EGNOS in new innovative rail operation with important market impact and with important effects on socio-economic, mobility and environment;

• Prepare markets for Galileo introduction since EGNOS is the precursor of GALILEO and enablers will be created including the awareness and preparation of the railway to immediately apply the new system; • Stimulate EU GNSS industry competitiveness in domains which are reputed (railway safety, railway integrated operations) for using mostly traditional ground-based technologies and conservative for global approach.

The overall objective provides life demonstrationto create impact and proof of evidence -validated and certified under the EU ruling and applied on the line Brasov -Zarnesti of the RCCF-TRANS (Romania).

State of the art of GNSS-based railway projects

The GPS related positioning safety integrity obtained with commercial receivers is already applicable. In the 2000's the LOCOPROL project has proposed special algorithms to use 1D intersection with rail track and to evaluate the integrity of positioning when taking into account the probabilistic incertitude of GPS constellation [START_REF] Marais | A new satellite-based fail-safe train control and command for low density railway lines[END_REF]. It showed that the SIL 4 integrity for positioning was achievable when the accuracy requirement is in ranges of 150m along the track. Unfortunately LOCOPROL did not apply the SoL (Safety-Of-Life) integrity. Industrial solutions have been tested in simulation conditions amongst which ALSTOM in the conception of LOCOPROL, BOMBARDIER that developed advanced use of track digital data, THALES with fusion of GNSS, 2D and 3D accelerometer and of on-board mechanical odometry, or ANSALDO, in the project RUNE [START_REF] Albanese | The RUNE project: Navigation performance of GNSSbased railway user navigation equipment[END_REF], that proposed the use of GNSS speed measurement in fusion with the train odometry to enhance the train odometry accuracy.

In relation with EGNOS performance in the railway environment, practical tests have been carried out in the projects GADEROS [START_REF] Prieto | Gaderos project field trials underway: a project is underway to apply global satellite navigation to safety-critical systems such as ERTMS and ETCS[END_REF] and GRAIL [START_REF] Urech | GRAIL, GNSS Introduction in the rail sector[END_REF]. The tests have been performed in the periods when EGNOS was only experimentally broadcasting (years 2006 -2008). The results can be conclusive but the absence of a live demonstration using the SoL in real train operations condition was still missing.

More recently, the project GRAIL [START_REF] Urech | GRAIL Final Activity Report[END_REF] has concluded that GNSS positioning and integrity performance (EGNOS as precursor and, notable Galileo) can be compatible with the ETCS odometry when using the GNSS receiver as a sensor, at the same level of confidence as the mechanical odometer and the Doppler radar. The GRAIL-2 will demonstrate the use of GNSS in this context (speed sensor complement to Doppler radar).

The rail sector in Europe has not yet adopted GNSS in safety-related applications. The barriers preventing the application of GNSS to rail safety have been identified within the UIC Galileo expert group (UIC, 2005):

• Missing the proof of evidence with practical and demonstrable means that sufficient safety integrity levels (SIL) can be obtained as global safety target in real train operations when GNSS is the primary source for location and speed information.

• Missing the proof of evidence that engineering and supply of flexible and scalable architectures for the onboard with train locators based on GNSS are available with affordable costs on a range of application categories such as LTL operations.

• Missing the proof of evidence that the conception of strategy for the validation of rail application with introduction of GNSS is applicable based on the multimodal validation of SIS-SoL (as per GALCERT programme) and the joint use of aviation and rail standards

The SATLOC project has been built as an answer to these identified barriers.

Objectives of the project

The different objectives of the project are described here above.

The elaboration and demonstration of innovative conception of GNSS use in the low traffic lines signalling and train control (primary railway safety).

The innovative conception of safely integrated signalling, train control and traffic management of the low traffic lines is based on GNSS (starting with EGNOS SoL integrity). The low traffic lines are the "E" lines according to the UIC classification, characterized by closed exploitation without -or with very limited-incidence on the main lines. The lines are low traffic density and have large headways of 20-30 minutes between trains. Freight trains are operated only occasionally and submitted to particular operational rules. The innovation consists in a new rail operation concept to realise full safety enforcement of movement authority through trains' speed and train control supervision (train's speed supervision equivalent to the ETCS functionality). The high achievable operation safety target, of 10 -9 train hazards/hthe same as the ETCS safety target -will apply the close-loop real time interaction -reciprocal check of safe states between trains' on board computer and the Radio Block Centre (RBC-TCC). This is enabled by the continuous train position and velocity determination with GNSS (EGNOS and in the future, GALILEO) and its process on-board and in the RBC to double-supervise the train safe state in a close-loop train regulation system. The large headways and the relative low speed of operating trains (maximum 120 km/h) enable the real-time safety cross-check on-board and in the RBC with smart utilisation of the radio transmission capacity, on a marginal cost. The innovation enables the direct use of EGNOS (GALILEO) positioning accuracy and integrity risk. This makes possible the cost-efficient integration of GNSS with SoL (EGNOS and in the future, GALILEO) into the safety layers of the integrated operation, signalling, train control and train movement management. The EGNOS integrity will be applied to satisfy the required level of safety integrity and availability of the railway service.

Enlargement of the GNSS application field to railway safety, with potential of application until ~ 35 -40% of the rail network in Europe and much higher in the world.

The innovative conception to use the on-board computer functions and radio-control centre functions in synergy and inter-connection to realise the full speed supervision train control on high safety level is actually revolutionary to demonstrate and conquest the GNSS access to rail safety. The project develops and applies innovative tools of "exportation" concept from the real-scale live demonstrator to other railway lines, based on optimised modularity and simulation of other local application conditions of GNSS and use of integrators to optimise cost, supply, commissioning and migration

Alignment of railway solutions for safety to the standards of EGNOS and GALILEO initially set to aviation.

The available GNSS integrity risk of 2,5*10 -7 (EGNOS integrity risk @ Alert Limit and Time to Alarm) will be directly applied within the safety chain of the railway operation. The SATLOC innovative conception demonstrates the capability of the ETCS conception to integrate the new technology on functionality equivalent to ETCS L2 without track-side signals and common migration to the future L3. The bases are the On-board and RBC-TCC platforms and full ETCS "language" and specifications (subset 026). SATLOC will reach the similar functionalities on a low cost base, cheaper than the current on-board and track-side ETCS applications. SATLOC LCC (Life Cycle Cost) targets will be analysed against the economic effects and business cases of relevant applications.

Creation and inclusion of fully innovative services of integrated rail traffic control and management, real-time information for passengers, increase of transport reliability and quality which are only enabled by the continuous trains' movement supervision with GNSS.

The innovative services address the optimisation of the traffic control and management integrated with the safe operation and fully real-time information from ONE central point for the whole operated line(s).

Other innovative conceptions are created and demonstrated:

• The innovative conception of the track-side train direction and safe crossing in the stations applies pre-routed sets of switches in crossing stations (spring and trail-able switches) to avoid complicated and costly interlocking. The innovation will also address the configuration of the RBC to realise the safe movement authority elaboration in connection with the closed-loop trains' movement control applied on all trains in the controlled area. This function is an advanced approach to the future ETCS level 3.

• The innovative tools for assessment, proof and validation of safety and the optimal use of GNSS and radio in locally determined conditions.

• The innovative conception to reach a full migration towards the ERTMS/ETCS conception when integrating the ERTMS Regional UIC specifications already applied in Sweden.

The project cooperates with the relevant drivers of the innovation in the field of GNSS and with the railway integrating and supply industry. The consortium includes the UIC and the railways, SIEMENS, INVENSYS-RAIL, ANSALDO STS, TELESPAZIO SPA, IFSTTAR, TU-Braunschweig, FH-WELS, SPIRENT PLC, and AFER-Romania (the railway safety authority of Romania). RCCF-TRANS Romania is the train operator and infrastructure manager who applies SATLOC on the pilot line. UIC assures the technical and managerial coordination of the project.

Operational and functional requirements

SATLOC enables the satisfaction of public service requirements of low traffic density lines, in terms of: • normal service, with an agreed timetable • safety target, approved by the safety authority, the same as the previous railway service, e.g. the use of the ALARP methodology to define the operational system safety target • regularity, quality, information • cost constraints, eventually derived from a business case evaluation of the line operation

The following operating requirements have been specified:

•

Allocation of the operational safety target

Currently the pilot line (and even a majority of the low traffic density lines) is secured either with the telephone block or with the old (~120 years old) SIEMENS (Frietsche) electric bloc (fig. 1).

The SATLOC project consortium has decided to use the ALARP approach to allocate the safety target for the train operation on demonstration line. This should mean that the new system (SATLOC) shall realize the same or higher safety target as the current employed system. This procedure is in accordance with European laws and regulations {European Commission 2009 #265}. Although the current safety function based on the mechanical interlocking and S&H bloc are not quantitatively qualified, the study of the safety case of the operations based on such equipment concludes on a THR of ~ 4*10 -6 /h. This results from the involvement of human responsibility with double check (two agents).

Fig. 1. S&H mechanical interlocking and block on the line Brasov-Zarnesti

If applying the ALARP, it should have been resulted that the safety target of SATLOC was inferior to the ETCS THR. Therefore, the SATLOC consortium has decided to adopt directly the safety target of the ETCS train operation. In the scope of consistency with the migration to the ETCS and moreover by force of using the general ETCS specification of RAMS and mainly Subset 026, it has been decided that the THR in the train operation on SATLOC lines will be the same as for the ETCS, i.e. 10 -9 /h for one train. This decision, in agreement with the safety authorities, was applicable in the context of advanced innovation, where the train and the track-side (On-board and RBC-TCC) are checking reciprocally, in close loop and in real time the accomplishment of the safety critical function of the system. This function (as also the ETCS function) is the enforcement of the Movement Authority, i.e. the safe stop of the train prior to the limits of the danger point. The integrity risk of GNSS/EGNOS positioning function is 2,5*10 -7 for each fix in open sky condition of visibility with a normal accuracy better than 3 m (typical 1 m with EGNOS augmentation). The functional algorithms of figure 2 have been implemented in the RBC -TCC taken into account the quasi-continuity of position and speed determination by GNSS.

Fig. 2. The Movement Authority survey and the train tracking modules in the TCC

The train tracking module is open and running for each train registered into the controlled area. The modules verify positioning accuracy achieved by GNSS and the on-board odometry for each train, using the route map as a sensor. If repeated anomalies are detected, the module emits a warning to the driver and can also trigger an automatic emergency brake. The movement authority survey module uses, for each train, the MA data, the route map data, which includes the line static profile, and the train data. The route map is a high integrity track-axis survey in absolute coordinates (Y, X, Z) with a minimum resolution of 5 m and verifiable (through alternative topometric methods) accuracy of 50 cm. The information of the static line profile is attached to each portion of the track. When reading the route map, both the train and the TCC shall determine the speed profile of the trains and also the "intervention points" for triggering the "attention" (warning) and, if the driver does not respect the speed reduction, the trigger of the "emergency brake". As a consequence, the train OB system and the TCC survey in real time if the train actually executes the speed control. If the train fails, then the TCC module shall warn the driver and automatically trigger the emergency brake. The reciprocal check and the interaction between the train and the TCC enable to accept lower safety integrity on each component. The interaction ensures the overall safety target that is a THR less than 2*10 -9 /h for a train.

Technical design and implementation

The SATLOC technical design has followed the standard procedures where the hardware and software architectures have been optimised from the points of view of:

• Achievement of the operational and functional requirements;

• Balance of the overall cost constraints, mainly determined by the integrity imposed to the software functions and the hardware safety architecture;

• Selection of equipment to achieve the RAM objectives

Train -TCC radio link. Migration towards independence from the radio bearer

Currently the TCS uses the GSM-R (rail dedicated communication system derived from the standard GSM). The GSM solution for the ETCS radio bearer has been selected in the 1992's. At that time the GSM was the most progressive digital mobile radio standard. 20 years after, the migration towards independence from the radio bearer is envisaged. SATLOC marks also in this aspect the innovative solutions. Tests are on-going to establish if any potential end-to-end delay does not exceed the real time constraints of the operational application. As an overall observation, the data transmission by tunnelled VPN and the application of EURORADIO (where each train will have a distinct encoding key) is superior from safety, security and availability to the GSM application. It is expected (and will be proven during the exploitation phase) that also the LCC of this solution is inferior to the GSM-R.

The tests already performed (when the on-board in laboratory of the Wels OOH has been connected via VPN with the TCC in the laboratory of INVENSYS U.K.) have shown no data latency and no unavailability challenges. The use of IP standards, already available in any performing telecommunication system makes possible the "intelligent" adaptation of the application to large class of radio bearer (including the satellite telecommunication). Fig. 6. VPN under UMTS bearer applied in front of the EURORADIO.

Laboratory and on site implementation and tests

The specification of laboratory tests is focused on demonstration of mock-up system functionality (including the key equipment and the application software):

• On board functions e.g. registration & deregistration of trains, receive and enforcement of MA where the "run" is simulated by reading the Route Map file with the "instant" speed of the train, functional display systems on the DMI and the TCC, other similar.

Conclusions and perspectives

Based on 15 years of experience and theoretical research of the UIC and of the SATLOC partners, the project started in January 2011 produces now good results. This paper has described the project in the continuity of the past European projects. A few months before the end of the project, SATLOC has shown the feasibility of the system on a real railway line.

It is now expected that the functional, operational and technical tests will produce an important database to actually evaluate the achievement of the objectives and that SATLOC may produce a turnover in the overall mentality in favor of using the absolute positioning of trains with GNSS for primary safety, in the train control. Essential will be the use of the Route Map (with a tentative of standardization) and the concept of virtual balises. It could be also understood that the migration of ETCS and SATLOC will reach soon a meet-point where the absolute positioning of trains, the use of route maps sent via the MA's and the concept of virtual balises for interoperability will join the two systems.

  Movement authority (MA) SATLOC Page 4 • Train control (TC) • Train separation (TS) • Full speed supervision • Train integritytrain completeness monitoring (TCM) ; (yet applied only for demonstration purpose) • Prevention of over-speed (POS) (is restricted to prevention on maximum line speed and on permanent speed restrictions) • Shunting (SH) • Control of movements (CMV) • Supervision of system's borders (SSB) • Control and supervision of level crossings (CLC) (NAP) • Protection of emergency personnel working on or directly adjacent to the track (PWP) (NAP) • stop to train(s)emergency stop command to the trains of a specific controlled area (ES) Requirements have been specified to the following operations envisaging safety: • Protection against train-to-train collisions (PATC) • Prevention of over-speed (POS) • Control of movements (CMV) • Control and supervision of points (C)simplified interlocking applied for low traffic density lines

Fig. 3 .

 3 Fig. 3. SATLOC reference architecture

Fig. 7 .

 7 Fig. 7. Laboratory test arrangementsThe laboratory tests did not target the demonstration of any "safety case" since the operational context is not available into the laboratory arrangement. The successful accomplishment of laboratory tests has concluded on the following: • The software components, although not perfect yet are suitable to be loaded on trains and Real TCC in Zarnesti > for tests with running trains • The suggestions made by AFER Romanian Rail Safety Authority have been approved: they consist of implementing on the TCC display a ranked "detail" selection to support with more information the traffic management including some degraded modes.

Fig. 8 .

 8 Fig. 8. SATLOC train during the real scale tests

Acknowledgements

The author would like to thanks the FP7 for funding this work.