Kevin Salesse
email: k.salesse@pacea.u-bordeaux1.fr

Elise Dufour

Dominique Castex

Velemínský Petr

Frédéric Santos

Hedvika Kuchařová

Jun Libor

Brůžek Jaroslav

Salesse Kevin

Dufour Élise

Castex Dominique

Santos Frédéric

Kuchařová Hedvika

Life history of the individuals buried in the St. Benedict cemetery (Prague, 15 th -18 th centuries): Insights from 14 C dating

Keywords: bioarchaeology, mobility, diet, carbonate, collagen

published or not. The documents may come

INTRODUCTION

Until the end of the eighteenth century, mortality crises were recurrent events that instigated important demographic, social, economic and cultural changes in European societies [START_REF] Beauvalet-Boutouyrie | Les crises de mortalité à l'époque moderne : sources et méthodes[END_REF]. According to historical documents, war, famine, infectious disease and natural disasters were typically the main causes of the high mortality rates [START_REF] Bulst | Maladies et société (XIIe-XVIIIe siècles). Actes du colloque de Bielefeld[END_REF][START_REF] Walter | Famine, disease and crisis mortality in early modern society[END_REF]. Research on past mortality crises, particularly those of epidemic natures, is relatively new in the fields of archaeology and physical anthropology and requires elaborate multidisciplinary work [START_REF] Castex | Identification and interpretation of historical cemeteries linked to epidemics[END_REF][START_REF] Castex | Identification and interpretation of historical cemeteries linked to epidemics[END_REF].

The extensive St. Benedict cemetery, located in the Old Town district of Prague (Czech Republic), was excavated as part of a rescue archaeology contract in 1971; this excavation yielded 845 skeletons and a large number of artifacts that are mostly associated with human remains [START_REF] Martinec | Pohřebiště při Kostele svatého Benedikta: Nálezové zprávy, Katalog hrobu[END_REF]. Based on archaeological and architectural evidences, five phases of inhumations dating from the 11 th to the 18 th centuries were identified by archaeologists [START_REF] Ječný | Historie a výzkum staroměstského bloku kolem kostela sv[END_REF][START_REF] Martinec | Pohřebiště při Kostele svatého Benedikta: Nálezové zprávy, Katalog hrobu[END_REF]. The fifth phase includes 462 individuals [START_REF] Ječný | Historie a výzkum staroměstského bloku kolem kostela sv[END_REF][START_REF] Martinec | Pohřebiště při Kostele svatého Benedikta: Nálezové zprávy, Katalog hrobu[END_REF] and was the only one that presented multiple graves (MG) (a multiple grave is a single grave containing several individuals buried at the same time; [START_REF] Leclerc | Sépulture[END_REF]). An initial exhaustive analysis of the human remains from the five phases was undertaken to understand the morphology, demography and pathology of the population living in Prague from the Middle Ages to the early modern period [START_REF] Hanáková | Pohřebiště kolem bývalého kostela Svatého Benedikta v Praze[END_REF]. This study did not attempt to relate the type of inhumation, individual (IG) versus multiple grave, or the nature of the mortality, attritional versus mass mortality [START_REF] Hanáková | Pohřebiště kolem bývalého kostela Svatého Benedikta v Praze[END_REF]. A new mortality profile obtained from a study of 120 individuals buried in 20 MG, half of the total number of MG, showed a very selective composition of the population [START_REF] Castex | Epidemic mortality crises of the past : bioarchaeological approach[END_REF]. Adolescent and young adult males were clearly over-represented, suggesting that a catastrophic event was the cause of the mortality of the MG individuals. The absence of lethal and traumatic injuries to the bones excluded violent deaths resulting from an act of war, massacre or natural disaster [START_REF] Castex | Epidemic mortality crises of the past : bioarchaeological approach[END_REF]. A mortality crisis linked to an epidemic disease was thus hypothesized to be the cause of the presence of the MG during the fifth phase of St. Benedict cemetery [START_REF] Castex | Epidemic mortality crises of the past : bioarchaeological approach[END_REF]. The current chronology based on archaeological findings and the evolution of the buildings, such as the St. Benedict Church dates the fifth phase to between 1635 and 1792 AD. During this period, the Order of Canons Regular of Prémontré (the "Premonstratensian Order") was the landowner of the site. Historical sources report two episodes of mass mortality, which occurred in 1639 AD (during the Thirty Years War) and in 1742 AD (during the Siege of Prague). There is no indication, however, of the burial locations for these two events, and it is not currently possible to identify which event caused the mortality crisis evidenced by the MG at the St. Benedict cemetery.

Stable isotope analysis conducted on human tissues preserved in archaeological sites can be used to characterize individual life histories with respect to dietary, environmental and geographical differences [START_REF] Knudson | Oxygen isotope analysis in a land of environmental extremes: the complexities of isotopic work in the Andes[END_REF][START_REF] Müldner | The 'Headless Romans': Multi-isotope investigations of an unusual burial ground from Roman Britain[END_REF]. Investigating the relationship between life history reconstruction and archaeological evidence (bioarchaeological information and funerary practices) can improve our knowledge of the history of the St.

Benedict site. The isotope values of carbon and nitrogen (δ 13 C and δ 15 N) from human tissues are used to reconstruct diet. The δ 13 C values differ between plants that use C3 and C4 photosynthetic pathways, and between terrestrial and marine resources [START_REF] Smith | Two categories of 13 C/ 12 C ratios for higher plants[END_REF]. The natural variations of δ 13 C values among plants and animals are maintained in the tissues of their consumers because carbon is incorporated in the food chain with an isotopic offset at each trophic level. Thus, the δ 13 C value of a consumer's collagen (δ 13 Ccol) is generally enriched by 5‰ relative to consumed plants and by 1‰ relative to consumed animals [START_REF] Deniro | Influence of diet on the distribution of carbon isotopes in animals[END_REF][START_REF] Van Der Merwe | 13 C content of human collagen as a measure of prehistoric diet in Woodland North America[END_REF][START_REF] Van Klinken | An overview of causes for stable isotopic variations in past European human populations: environmental, ecophysiological, and cultural effects[END_REF]. A fractionation between the δ 13 C values of structural carbonate in bone (δ 13 Csc (bone)) or tooth enamel (δ 13 Csc (enamel)) and diet of approximately 12‰ has been determined for pigs and appears to be suitable for generalization to humans [START_REF] Harrison | Paleodiet studies using stable carbon isotopes from bone apatite and collagen: Examples from Southern Ontario and San Nicolas Island, California[END_REF][START_REF] Passey | Carbon isotope fractionation between diet, breath CO2, and bioapatite in different mammals[END_REF][START_REF] Schwarcz | Stable carbon isotope analysis and human diet[END_REF]. The δ 13 Ccol values mainly reflect the carbon in the dietary protein, whereas the δ 13 Csc (bone) or δ 13 Csc (enamel) values represent an average of the carbon inputs from the whole diet i.e. from the primary macronutrients, proteins, carbohydrates and lipids [START_REF] Ambrose | Experimental evidence for the relationship of the carbon isotope ratios of whole diet and dietary protein to those of bone collagen and carbonate[END_REF][START_REF] Jim | Stable carbon isotopic evidence for differences in the dietary origin of bone cholesterol, collagen and apatite: Implications for their use in palaeodietary reconstruction[END_REF][START_REF] Tieszen | Effect of diet quality and composition on the isotopic composition of respiratory CO2, bone collagen, bioapatite, and soft tissues[END_REF]. The difference between δ 13 Csc (bone) and δ 13 Ccol (Δ 13 Csc-col (bone)) mainly reveals information regarding the δ 13 C values of the protein and non-protein portions in the diet (e.g., [START_REF] Ambrose | Experimental evidence for the relationship of the carbon isotope ratios of whole diet and dietary protein to those of bone collagen and carbonate[END_REF][START_REF] Tieszen | Effect of diet quality and composition on the isotopic composition of respiratory CO2, bone collagen, bioapatite, and soft tissues[END_REF]. δ 15 N values in bone collagen (δ 15 Ncol) have been used to investigate the importance of marine protein in past human diets [START_REF] Chisholm | Stable carbon isotope ratios as a measure of marine versus terrestrial protein in ancient diets[END_REF][START_REF] Schoeninger | Stable nitrogen isotope ratios of bone collagen reflect marine and terrestrial components of Prehistoric human diet[END_REF], as well as to infer the trophic position by considering the step-wise enrichment of approximately 3-5‰ between the consumer's diet and its tissues [START_REF] Bocherens | Trophic level isotopic enrichment of carbon and nitrogen in bone collagen: case studies from recent and ancient terrestrial ecosystems[END_REF][START_REF] Deniro | Influence of diet on the distribution of nitrogen isotopes in animals Geochim[END_REF][START_REF] Schoeninger | Nitrogen and carbon isotopic composition of bone collagen from marine and terrestrial animals[END_REF]. However, the δ 15 Ncol values can be affected by many factors such as pregnancy [START_REF] Fuller | Nitrogen balance and δ 15 N: Why you're not what you eat during pregnancy[END_REF], breastfeeding [START_REF] Fuller | Detection of breastfeeding and weaning in modern human infants with carbon and nitrogen stable isotope ratios[END_REF], growth [START_REF] Trueman | The effect of growth rate on tissue-diet isotopic spacing in rapidly growing animals. An experimental study with Atlantic salmon (Salmo salar)[END_REF], diseases [START_REF] Katzenberg | Stable isotope variation in pathological bone[END_REF], starvation [START_REF] Mekota | Serial analysis of stable nitrogen and carbon isotopes in hair: monitoring starvation and recovery phases of patients suffering from anorexia nervosa[END_REF], field manuring [START_REF] Bogaard | The impact of manuring on nitrogen isotope ratios in cereals: Archaeological implications for reconstruction of diet and crop management practices[END_REF] and arid environment conditions [START_REF] Thompson | Isotopic palaeodiet studies of ancient Egyptian fauna and humans[END_REF]. The geographic origin and potential movements of humans during their lifespans can be inferred from the oxygen isotope analysis (δ 18 O) of structural carbonate in bone (δ 18 Osc (bone)) and tooth enamel apatite (δ 18 Osc (enamel)) [START_REF] Schwarcz | Oxygen isotopic analysis as an indicator of place of origin[END_REF][START_REF] Sealy | An historic skeleton from the slave lodge at Vergelegen[END_REF][START_REF] White | Oxygen isotopes and the identification of geographical origins: the valley of Oaxaca versus the valley of Mexico[END_REF]. Diachronic changes of residence, particularly between the childhood age and the few last years before the death, can be studied through the difference between δ 18 Osc (bone) and δ 18 Osc (enamel) values (Δ 18 Osc (bone-enamel)). Oxygen in the tissues is in equilibrium with the body's water oxygen pool, which derives primarily from drinking water, inhaled vapor water and food sources [START_REF] Longinelli | Oxygen isotopes in mammal bone phosphate: A new tool for paleohydrological and paleoclimatological research?[END_REF][START_REF] Luz | Fractionation of oxygen isotopes between mammalian bone-phosphate and environmental drinking water[END_REF].

Drinking water stems from surface water (e.g., lakes and rivers) and groundwater (e.g., wells and springs) sources that are fed by precipitation (e.g., rain and snow) and water from the catchment area. The δ 18 O values of the river waters predominantly reflect the δ 18 O values of the mean annual recharge and, to a lesser extent, the local precipitation [START_REF] Bowen | Stable hydrogen and oxygen isotope ratios of bottled waters of the world[END_REF][START_REF] Kendall | Distribution of oxygen-18 and deuterium in river waters across the United States[END_REF]. The δ 18 O values of the environmental waters (e.g., surface water, groundwater and precipitation) are link to climate and physical factors, such as altitude, latitude and distance from the coast [START_REF] Dansgaard | Stable isotopes in precipitation[END_REF][START_REF] Gat | Oxygen and hydrogen isotopes in the hydrologic cycle[END_REF] leading to predictable variations over a continuous landmass.

The present study aims to identify the mass mortality episode that resulted in the death of the MG individuals during the last inhumation phase of the St. Benedict cemetery by comparing the reconstructed life histories of the IG and MG individuals and refining the current dating of the two inhumation types. The homogeneity and identification of local Bohemian individuals and foreigners were examined using stable isotope analyses (i.e., δ 13 C, δ 15 N and δ 18 O) conducted on different tissues (i.e., bone collagen, bone carbonate and enamel carbonate), archaeological data, and direct 14 C dating of human bone collagen.

MATERIALS AND METHODS

Sample collection

A total of 31 individuals buried in the fifth occupation phase of the St. Benedict cemetery in Prague were selected. This sample was composed of 12 individuals from IG, 9 individuals from multiple grave 1 (MG1), 9 individuals from multiple grave 2 (MG2), and 1 individual from multiple grave 3 (MG3) (Fig. 1). The skeletons were preserved in their integrity and bones did not present macroscopic alteration. The individuals buried in IG were randomly selected, whereas those from MG1, MG2 and MG3 (MG1-2-3) were selected according to the location and size of the grave. The three MG were located to the northwest of the St. Benedict Church (Fig. 1). The MG1 and MG2 contained the largest number of skeletons of all graves in this sector. Individuals were sexed by combining primary and secondary sexual diagnoses using the pelvic bones [START_REF] Brůžek | A method for visual determination of sex, using the human hip bone[END_REF][START_REF] Brůžek | Identification biologique individuelle en paléoanthropologie. Détermination du sexe et estimation de l'âge au décès à partir du squelette[END_REF][START_REF] Murail | DSP : a tool for probabilistic sex diagnosis using worldwide variation in hip-bone measurements[END_REF] and others bones such as the cranium, mandible and femur [START_REF] Castex | La détermination sexuelle des séries archéologiques : la validité de certains caractères osseux «extra-coxaux[END_REF]Martin, 1914;[START_REF] Murail | A new approach to sexual diagnosis in past populations. Practical adjustments from Van Vark's procedure[END_REF]. Different methods were used for estimating age-at-death for immature individuals (Moorrees et al.,1963a,b;[START_REF] Birkner | L'image radiologique typique du squelette : aspect normal et variantes chez l'adulte et l'enfant[END_REF][START_REF] Scheuer | Developmental juvenile osteology[END_REF] and adults [START_REF] Owings-Webb | Epiphyseal union of the anterior iliac crest and medial clavicle in a modern multiracialsample of American males and females[END_REF][START_REF] Schmitt | Estimation de l'âge au décès des sujets adultes à partir du squelette : des raisons d'espérer[END_REF]. Our sample consisted of 5 females, 20 males and 6 individuals of unknown sex (Table 1). With the exception of 3 immature individuals, all of the individuals were adults (Table 1). For each individual, we sampled the permanent second molar (M2) and a piece of the cortical bone from the femur. This sampling strategy allowed for a diachronic approach given that the M2 forms between 3 and 8 years of age and is not remodeled once it is formed (Moorrees et al., 1963a), whereas the femur undergoes constant remodeling, with a complete bone replacement time of 10 to 30 years (Hedges et al., 2007;[START_REF] O'connell | Isotopic comparison of hair, nail and bone: Modern analyses[END_REF]. All the skeletons were curated in the Department of Anthropology at the National Museum in Prague.

No fauna were found at the St. Benedict site; therefore, no direct comparison between contemporaneous human and animal isotopic values could be performed to estimate the proportions of the different food resources and the isotopic values of the drinking water.

Moreover, there were no environmental isotopic data available in the literature for the early modern period of the Czech Republic to provide the local range of isotope values. Three teeth from cows, two teeth from pigs and one tooth from a goat were selected from the site of the fortified gate of the Old Town district in Prague (13 th -14 th centuries) to estimate the local range of environmental δ 18 O values.

Bone and enamel apatite preparations and analysis

Tooth calculus, cancellous bone and the superficial layer of compact bone were removed using a tungsten carbide dental tool to eliminate the possible presence of adsorbed diagenetic carbonates. Enamel powder was recovered from the crown using a diamond drill bit. For each sample, approximately 10 mg of enamel powder was treated as described by [START_REF] Balasse | The seasonal mobility model for prehistoric herders in the south-western Cape of South Africa assessed by isotopic analysis of sheep tooth enamel[END_REF]. This powder was first soaked in 2-3% NaOCl solution (0.1 ml solution/mg sample) at room temperature for 24 h to oxidize the organic matter and was subsequently rinsed five times with distilled water. The remaining fraction was treated with 0.1 M CH3COOH for 4 h to eliminate exogenous and adsorbed carbonate and was then rinsed five times with distilled water. Next, the enamel powder was either freeze-dried for 90 min at -87°C or oven-dried for 18 h at 65°C. The purification process resulted in an average loss of 30% of the initial sample weight. The bone samples were ground to a powder using either an electric grinder or an agate mortar and pestle. Chemical bioapatite purification was performed on 15-25 mg of bone powder using the same protocol as were used to purify the tooth enamel, except that the bone powder was treated with 1 M CH3COOH for 1 h to eliminate exogenous adsorbed carbonate. The purification process resulted in an average loss of 78% of the initial sample weight. Bone and enamel apatite preparations were conducted at the Muséum National d'Histoire Naturelle (MNHN) in Paris. Apatite powder (580-630 μg) was weighed and reacted with 100% H3PO4 at 70°C in a Kiel IV device interfaced to a Delta V Advantage (Thermo Scientific) isotope ratio mass spectrometer at the Service de Spectrométrie de Masse Isotopique at the MNHN (SSMIM) to determine the δ 13 C and δ 18 O values. Over the period of analysis of these carbonate samples, 46 analyses of the SSMIM internal carbonate standard (Marble LM) were analyzed and provided a mean δ 13 C value of 2.13 ± 0.02‰ (theoretical δ 13 C value normalized to NBS-19 = 2.13‰) and a mean δ 18 O value of -1.84 ± 0.09‰ (theoretical δ 18 O value normalized to NBS-19 = -1.83‰).The analytical precision within each run, measured from 6 to 8 analyses of the standard Marble LM, varies from 0.01 to 0.02‰ for δ 13 C and from 0.04 to 0.07‰ for δ 18 O.

Bone collagen extraction and analysis

The cleaned bone was ground to a powder with an electric grinder to obtain a grain size of 0.7 mm. Collagen was extracted following [START_REF] Longin | New method of collagen extraction for radiocarbon dating[END_REF] protocol modified by [START_REF] Brown | Improved collagen extraction by modified Longin method[END_REF] and [START_REF] Bocherens | Isotopic biogeochemistry ( 13 C, 15 N) of fossil vertebrate collagen: application to the study of a past food web including Neandertal man[END_REF]. Approximately 200 mg of powdered bone was soaked in 20 ml of 1 M HCl solution for 20 min at room temperature for decalcification and then filtered through a MF-Millipore 5 μm filter. The residue was soaked into 0.125 M NaOH for 20 h to remove potential contamination of fulvic and humic acids. After filtration, it was soaked into 0.01 M HCl (pH = 2) in a sealed tube at 100°C for 17 h for solubilization, filtered again and freeze-dried at -87°C for 24 to 36 h. Bone collagen extraction was conducted at the MNHN. Samples (0.4-0.5 mg) were combusted using an Elemental Analyser Flash 2000 coupled to a Delta V Advantage (Thermo Scientific) isotope ratio mass spectrometer at the SSMIM for δ 13 C and δ 15 N analysis. Over the sample run, 8 samples of the IAEA-600 international standard were analyzed and provided a mean δ 13 C value of -27.77 ± 0.34‰ and a mean δ 18 O value of 1.00 ± 0.02‰.

Diagenetic alteration indicators

Several indicators have been developed to assess potential diagenetic alterations or contaminations of the bone collagen. The atomic C:N ratio [START_REF] Deniro | Postmortem preservation and alteration of in vivo bone collagen ratios in relation to palaeodietary reconstruction[END_REF], the collagen yield from the whole bone (wt %) [START_REF] Ambrose | Preparation and characterization of bone and tooth collagen for isotopic analysis[END_REF] and the percent of carbon (%C) and nitrogen (%N) in the extract [START_REF] Ambrose | Preparation and characterization of bone and tooth collagen for isotopic analysis[END_REF] were used to check the state of the collagen preservation. The atomic C:N ratio of unaltered bone collagen ranges from 2.9 and 3.6 [START_REF] Deniro | Postmortem preservation and alteration of in vivo bone collagen ratios in relation to palaeodietary reconstruction[END_REF]. Fresh bone contains approximately 22 wt % collagen, which consists of 34 to 43% of carbon and 11 to 16% of nitrogen [START_REF] Van Klinken | Bone collagen quality indicators for palaeodietary and radiocarbon measurements[END_REF]. The δ 13 Ccol and δ 15 Ncol values remain constant until bone collagen yields fall to less than 1% of the total bone mass [START_REF] Dobberstein | Archaeological collagen: Why worry about collagen diagenesis?[END_REF]. The percent of carbon and nitrogen in unaltered bone collagen should exceed 13% and 4.8%, respectively [START_REF] Ambrose | Preparation and characterization of bone and tooth collagen for isotopic analysis[END_REF]. Unlike for bone collagen, there is no well-established indicator to assess the preservation of structural carbonate in bone and enamel apatite [START_REF] Shin | Diagenesis in bone and enamel apatite carbonate; the potential of density separation to assess the original composition[END_REF]. However, different tests can be performed to detect potential diagenetic effects on structural carbonate isotopic values. First, based on the assumption that bone apatite is more sensitive to recrystallization and highly susceptible to postmortem changes in comparison with enamel apatite a pairwise comparison of δ 13 Csc (bone) and δ 13 Csc (enamel) values and of δ 18 Osc (bone) and δ 18 Osc (enamel) values can be done for detecting a preferential effect on bone structural carbonates. Second, the δ 13 Csc (bone) and δ 18 Osc (bone) values can be compared with the bone collagen yields to assess the influence of collagen loss on structural carbonate.

Radiocarbon dating

Eight human bone collagen samples from IG and MG (Table 6) were prepared for AMS 14 C dating at the AMS C-14 Labor Erlangen (Germany) and the Oxford Radiocarbon Accelerator Unit (England) using routine collagen extraction procedures [START_REF] Bronk Ramsey | Radiocarbon dates from the Oxford AMS System: Archaeometry datelist 30[END_REF][START_REF] Longin | New method of collagen extraction for radiocarbon dating[END_REF]. Dates were calibrated using the IntCal09 calibration curve and Cal Rev 6.1.0 software [START_REF] Reimer | IntCal09 and Marine09 radiocarbon age calibration curves, 0-50,000 years cal BP[END_REF]Stuiver and Reimer, 1993).

Statistical analysis

The statistical R package (version 2.10, R Development Core Team, 2010) and the software Statistica © 7.1 were used for statistical computations and graph generations. We used non-parametric Mann-Whitney U tests to determine whether our groups of IG, MG1, MG2 and MG3 samples came from the same population. Additionally, we used multivariate analysis of variance (MANOVA), decision tree learning and mixed-data factor analysis (MDFA) to test for homogeneity and the distance between the IG, MG1, MG2 and MG3 groups across all of the qualitative and quantitative variables.

RESULTS

Sample preservation

The bone collagen atomic C:N ratios show low variability, ranging from 3.1 to 3.3 (mean = 3.2 ± 0.1) (Table 2). The carbon and nitrogen concentrations in bone collagen range from 38.5 to 43.2% (mean = 41.3 ± 1.3%) and from 13.7 to 16% (mean = 15.1 ± 0.6%), respectively (Table 2). The bone collagen yields show a large variability, ranging from 4.2 to 22.2 % (mean = 14.1 ± 6.1%) (Table 2). There is a very low correlation (R² = 0.37) and no correlation (R² = 0.1) between collagen yield and the δ 18 Osc (bone) and the δ 13 Csc (bone) values, respectively. Pairwise comparisons between the δ 13 Csc (bone) and δ 13 Csc (enamel) values (Fig. 2) as well as between the δ 18 Osc (bone) and δ 18 Osc (enamel) values do not show any trend of variation (Fig. 3). For the whole sample set, bone samples do not present more homogeneous δ 18 O and δ 13 C values than enamel samples (Figs. 23).

Stable isotope results

Human bone collagen

The mean bone collagen values for all of the groups combined are -19.7 ± 0.5‰ and 10.7 ± 1.6‰ for δ 13 Ccol and δ 15 Ncol, respectively (Table 1).

The mean δ 13 Ccol values are -19.6 ± 0.4‰ for IG, -20.0 ± 0.6‰ for MG1 and -19.6 ± 0.6‰ for MG2. The δ 13 Ccol value is -19.7‰ for MG3 (Fig. 4). Only IG and MG1 are significantly different with regard to the δ 13 Ccol value (Mann-Whitney = 0.04) (Table 4). The mean δ 15 Ncol values are 12.2 ± 0.9‰ for IG, 10.3 ± 0.7‰ for MG1 and 9.2 ± 1.2‰ for MG2. The δ 15 Ncol value is 9.3‰ for MG3 (Fig. 4). All of the groups are significantly different with regard to the δ 15 Ncol value (Mann-Whitney p < 0.05) (Table 4). The mean bone collagen values for MG1-2-3 are -19.8 ± 0.6‰ and 9.7 ± 1.1‰ for δ 13 Ccol and δ 15 Nco, respectively.

Human bone apatite

The mean bone carbonate values for all of the groups combined are -12.5 ± 1.3‰ and -4.7 ± 0.7‰ for δ 13 Csc (bone) and δ 18 Osc (bone), respectively (Table 1). The mean δ 13 Csc (bone) values are -13.5 ± 1.3‰ for IG, -12.2 ± 0.6‰ for MG1 and -11.5 ± 0.9‰ for MG2. The δ 13 Csc (bone) value is -12.4‰ for MG3 (Fig. 5). There are significant differences for the δ 13 Csc (bone) value between IG and MG1 (Mann-Whitney = 0.02) and between IG and MG2 (Mann-Whitney = 0.00), but there is no difference between MG1 and MG2 (Table 4). The mean δ 18 Osc (bone) values are -4.2 ± 0.7‰ for IG, -5.0 ± 0.5‰ for MG1 and -4.8 ± 0.5‰ for MG2 (Fig. 5). The δ 18 Osc (bone) value is -6.0‰ for MG3. Only IG and MG1 are significantly different with regard to the δ 18 Osc (bone) value (Mann-Whitney = 0.00) (Table 4). The mean bone carbonate values for MG1-2-3 are -11.9 ± 0.8‰ and -5.0 ± 0.5‰ for δ 13 Csc (bone) and δ 18 Osc (bone), respectively.

Human enamel apatite

The mean enamel carbonate values for all of the groups combined are -13.2 ± 0.7‰ and -4.8 ± 0.9‰ for δ 13 Csc (enamel) and δ 18 Osc (enamel), respectively

(Table 1). The mean δ 13 Csc (enamel) values are -13.6 ± 0.4‰ for IG, -12.9 ± 0.6‰ for MG1 and -12.8 ± 0.9‰ for MG2. The δ 13 Csc (enamel) value is -12.9‰ for MG3 (Fig. 6). There are significant differences for the δ 13 Csc (enamel) value between IG and MG1 (Mann-Whitney = 0.01) and between IG and MG2 (Mann-Whitney = 0.01), but there is no difference between MG1 and MG2 (Table 4). The mean δ 18 Osc (enamel) values are -4.0 ± 0.5‰ for IG, -4.9 ± 0.7‰ for MG1 and -5.5 ± 0.7‰ for MG2 (Fig. 6). The δ 18 Osc (enamel) value is -5.8‰ for MG3. There are significant differences for the δ 18 Osc (enamel) value between IG and MG1 (Mann-Whitney = 0.01) and between IG and MG2 (Mann-Whitney = 0.00), but there is no difference between MG1 and MG2 (Table 4). The mean enamel carbonate values for MG1-2-3 are -12.9 ± 0.7‰ and -5.3 ± 0.7‰ for δ 13 Csc (enamel) and δ 18 Osc (enamel), respectively.

Animal enamel apatite

The δ 18 Osc (enamel) values range from -10.3 to -7.3‰. The mean δ 18 Osc (enamel) value is -8.3 ± 1.1‰ (Table 3).

Comparison between tissues

The mean difference between δ 13 C values measured in bone carbonate and collagen (Δ 13 Csc (bone-enamel)) is 6.1 ± 1.5‰ and 7.9 ± 0.9‰ for IG and MG1-2-3, respectively (Table 1). The mean difference between δ 13 C values measured in bone and enamel carbonate (Δ 13 Csc (bone-enamel)) is 0.1 ± 1.5‰ and 1.0 ± 1.0‰ for IG and MG1-2-3, respectively (Table 1). The mean difference between δ 18 O values measured in bone and enamel carbonate (Δ 18 Osc (bone-enamel)) is -0.2 ± 0.9‰ and the 0.3 ± 0.6‰ for IG and MG1-2-3, respectively (Table 1).

Statistical comparisons

MG1, MG2 and MG3 are not significantly different from each other according to the isotopic dataset (MANOVAs, p > 0.05). Therefore, they form a single group (MG1-2-3). MG1-2-3 is significantly different from IG (MANOVA, p < 0.05).

There are no significant differences between the three MG with respect to age and sex (MANOVAs, p < 0.05). However, MG1-2-3 is distinct from IG with respect to age (younger or older than 30 years) and sex (MANOVAs, p > 0.05) (Table 5). The decision tree learning analysis highlights the separation between MG1-2-3 and IG, as well as the homogeneity within each group regarding the isotopic variables. The MDFA performed on the isotopic and bioarchaeological (sex and age) data confirms the distinction between MG1-2-3 and IG (Fig. 7). The first three components explain 71.4% of the variance, and the most significant and correlated variables are the δ 18 Osc (bone), δ 13 Csc (enamel), δ 18 Osc (enamel) and δ 15 Ncol values and sex.

C dates

Calibrated intervals at 2σ (95.4% confidence) fall in the ranges of 1476-1662, 1030-1208 and 1449-1635 cal AD for H36, H193 and H270, respectively, who were buried in the three IG. The intervals are 1685-1954, 1659-1952 and 1683-1954 cal AD for H60, H83 and H797, respectively, from MG1 and 1668-1953 for H75 from MG2 (Table 6). In addition, although the individual H421 from a different IG provides a calibrated radiocarbon date of 1486-1950 with a confidence interval of 95.4% (Table 6), 94%

of this probability distribution ranges between 1486 and 1669 cal AD.

DISCUSSION

Sample diagenesis

All the bone collagen indicators used to assess the influence of the diagenesis on the stable isotope values show that the bone collagen samples from the St. Benedict cemetery are well preserved. Regarding structural carbonate that is considered as highly susceptible to diagenetic alteration, the lack of correlation between the δ 13 Csc (bone) or δ 18 Osc (bone) values and the collagen yield indicates that collagen loss has no influence on its isotopic values. An important isotopic exchange between human remains and diagenetic fluids from the burial environment is expected to erase part the natural isotopic inter-individual variability (related to difference in life histories and age) by impressing the values of the diagenetic pole (Lecuyer et al., 2003;[START_REF] Amiot | Latitudinal temperature gradient during the Cretaceous Upper Campanian-Middle Maastrichtian: δ 18 O record of continental vertebrates[END_REF]. Because bone is less resistant to diagenesis than enamel, the biogenic signal of bone structural carbonate is more prone to be replaced by that of the diagenetic pole. In fact, the inter-individual variability of structural carbonate values is similar to that of enamel and there not tendency in the isotopic difference inδ 13 C and δ 18 O between the two tissues. Although it is not possible to totally exclude postmortem changes, these results indicate that δ 13 Csc and δ 18 Osc values of bone and enamel were not significantly affected by diagenesis and can be used for reconstructing life histories of the St. Benedict cemetery individuals.

Life history of the St. Benedict population

The exhibited by the individuals from MG1-2-3 indicate that the protein source is 13 C-depleted compared to the whole diet [START_REF] Kellner | A simple carbon isotope model for reconstructing prehistoric human diet[END_REF], suggesting a diet predominantly composed by a mixture of C3 and C4 energies (i.e. non-protein components of diet) as well as C3 protein (Fig. 8). In contrast, the relatively low Δ 13 Csc-col (bone) values (< 7‰) exhibited by the IG individuals indicate that the protein component of their diet is more 13 C-enriched than the whole diet [START_REF] Kellner | A simple carbon isotope model for reconstructing prehistoric human diet[END_REF], suggesting a diet comprising mainly C3 energy and C3 protein (Fig. 8). There is a significant negative relationship (p < 0.01) between [START_REF] Dufour | Palaeodietary implications of isotopic variability in eurasian lacustrine fish[END_REF][START_REF] France | Stable nitrogen isotopes in fish: literature synthesis on the influence of ecotonal coupling[END_REF]. Because the IG individuals do not present high δ 13 C values, the preferential consumption of freshwater resources is more likely (Fig. 8).

Δ
Alternatively, relatively high δ 15 Ncol values of the IG individuals might result from a nutritional or physiological stress [START_REF] Fuller | Nitrogen balance and δ 15 N: Why you're not what you eat during nutritional stress[END_REF]. However, a short-term dietary change caused by an episode of starvation is unlikely to be identified in the isotopic values of adult cortical bone collagen [START_REF] Beaumont | Victims and survivors: Stable isotopes used to identify migrants from the Great Irish Famine to 19th century London[END_REF]. Bone undergoes constant turnover and its isotope composition reflect average diet over approximately a decade (Hedges et al., 2007).

Only regular dietary stress due to chronic illness may modify significantly the δ 15 Ncol values [START_REF] Katzenberg | Stable isotope variation in pathological bone[END_REF]. IG were randomly selected in the St. Benedict cemetery and it is unlikely that they all shared the same chronic illness. In addition, there was no evidence of pathological lesions on the studied skeletons. Low protein intakes over life could explain the lowest δ 15 Ncol values exhibited by MG individuals. Nevertheless, a rich protein diet based on immature herbivores, herbivores consuming manured crops or freshwater resources is suggested for most individuals from the St. Benedict cemetery.

Comparison of the bone and enamel carbonate δ 18 O values and δ 18 O values from the environmental water sources was used to study the residential mobility across the lifespan and to identify local and foreign-born individuals [START_REF] Keenleyside | Oxygen isotopic evidence of residence and migration in a Greek colonial population on the Black Sea[END_REF]. The δ 18 Osc (bone) and δ 18 Osc (enamel) values are relatively homogeneous within each grave type. IG individuals have higher δ 18 Osc (bone) and δ 18 Osc (enamel) values than MG1-2-3 individuals (Fig. 9). values from the bone carbonate range from -7.7 to -4.7‰ (mean = -6.3 ± 1.1‰) for IG and from -9.3 to -6.0‰ (mean = -7.6 ± 0.9‰) for MG1-2-3 (Table 7). Although the spatial distribution of the δ 18 O values in meteoric water (δ 18 Omw), groundwater (δ 18 Ogw) and surface waters is well-known for Western and Southern Europe [START_REF] Longinelli | Isotopic composition of precipitation in Italy: A first overall map[END_REF][START_REF] West | Isoscapes: Understanding movement, pattern and process on Earth through isotope mapping[END_REF], no regional-scale distribution or isopleths of δ 18 Omw and δ 18 Ogw are available for Central Europe. However, the δ 18 Ogw values near Prague can be estimated from a compilation of different works [START_REF] Jiráková | Carbon isotopes to constrain the origin and circulation pattern of groundwater in the north-western part of the Bohemian Cretaceous Basin (Czech Republic)[END_REF][START_REF] Möller | Rare earth elements, yttrium and H, O, C, Sr, Nd and Pb isotope studies in mineral waters and corresponding rocks from NW-Bohemia, Czech Republic[END_REF][START_REF] Noseck | Carbon chemistry and groundwater dynamics at natural analogue site Ruprechtov, Czech Republic: Insights from environmental isotopes[END_REF][START_REF] Pačes | Magmatic and fossil components of thermal and mineral waters in the Eger River continental rift (Bohemian massif, central Europe)[END_REF][START_REF] Šilar | Using environmental isotopes for groundwater flow analysis in basinal structures[END_REF], and the δ 18 Omw values can be estimated using the highresolution global and regional mapping model OIPC (http://www.waterisotopes.org; [START_REF] Bowen | The Online Isotopes in Precipitation Calculator (OIPC), version 2.2[END_REF][START_REF] Bowen | Spatial distribution of δ 18 O in meteoric precipitation[END_REF]. According to these data sources, the local δ 18 Ogw values range from -11.2‰ to -8.6‰ with a mean value of -9.8 ± 0.6‰ and an annual mean δ 18 Omw value of -8.9‰ ± 0.4‰. This range of values falls into the range of European regions, such as Bohemia (between -12‰ and -7‰), Saxony (between -10‰ and -8‰) and France (between -13‰ and -4‰) (Fig. 9). Additionally, we used the equation developed by [START_REF] Amiot | Latitudinal temperature gradient during the Cretaceous Upper Campanian-Middle Maastrichtian: δ 18 O record of continental vertebrates[END_REF] (for all mammals excepted marsupials) and the δ 18 Oen values of the six animals from the fortified gate of the Old Town district in Prague to define the environmental δ 18 O values of the Prague region (Table 3). The δ 18 Odw values range from -10.3 to -8.0‰ (mean = -9.1 ± 1.1‰) for cattle and from -7.7 to -7.3‰ (mean = -7.5 ± 0.3‰) for pigs whereas the

Chronology of inhumation

Radiocarbon dating of human bone collagen indicates that IG individuals date from 1030 to 1669 AD, whereas MG1-2-3 individuals date from 1659 to 1954 AD. There is no overlap between the age ranges of MG1-2-3 (H60, H75, H83 and H797) and the age ranges of IG (H36, H193 and H270). We note that H193 predates H36, H270 and H421 and is most likely from an older occupation phase. Moreover, we know that the St. Benedict site was desecrated and demolished in 1792 [START_REF] Ardura | Prémontrés. Histoire et spiritualité[END_REF]. There is a small overlap of approximately 10 years between H421 (IG) and H83 (MG1). These data suggest two distinct inhumation phases for IG (15 th -17 th centuries AD) and MG1-2-3 (17 th -18 th centuries AD).

History of the fifth occupation phase of St. Benedict cemetery

Stable isotope analysis (δ 13 C, δ 15 N, δ 18 O) and 14 C dating challenge previous knowledge regarding the history of the last phase of use of the St. Benedict cemetery.

According to historical sources, St. Benedict was used as a cemetery until the early 17 th century [START_REF] Ardura | Prémontrés. Histoire et spiritualité[END_REF]. Premonstratensian chronicles and parish registers make no mention of inhumations in the cemetery after the settlement of the Premonstratensian canons at the St.

Benedict site and the funeral protest ban in 1635 (DJ IV 1, 1637-1736; DJ IV 2, 1736-1785).

However, the radiocarbon dates of MG1-2-3 contradict the historical data and suggest that the St. Benedict cemetery was briefly reused between the 17 th and 18 th centuries. Several buttons from clothing were found with the MG1-2-3 skeletons (Libor Jun, unpublished data), and they were identified as belonging to military uniforms, most likely dating from the 17 th and 18 th centuries [START_REF] Bleckwenn | Die friderizianischen Uniformen[END_REF][START_REF] Karger | Die entwicklung der adjustierung, rüstung und bewaffnung der österreichischungarischen armee 1700-1809[END_REF]. The presence of soldiers in St. Benedict cemetery is further supported by the selective composition of the MG population, as it was composed of young adult males [START_REF] Castex | Epidemic mortality crises of the past : bioarchaeological approach[END_REF]. 14 C dates support the hypothesis that an episode of mass mortality was caused by the siege of Prague. The siege of Prague occurred during the War of the Austrian Succession when the French-Bavarian-Saxon armies took control of Prague between 1741 and 1742. The population suffered considerable stress (Anonymous, 1863;[START_REF] Major | Lehrbuch der anthropologie in systematischer darstellung[END_REF][START_REF] Vlnas | Lumières et ténèbres : art et civilisation du baroque en Bohême[END_REF]. The Habsburg forces besieged the city and placed an embargo on foodstuffs and fodders [START_REF] Macek | Histoire de la Bohême des origines à 1918[END_REF]. The lack of essential nutrients and medical care, as well as poor hygienic conditions, was the breeding ground for the development of infectious diseases and epidemics. The Premonstratensian College, which is named the Norbertinum, was converted into a military infirmary to take care of dying soldiers (DJ IV 1, 1637-1736; DJ IV 2, 1736-1785). Given the large number of soldier bodies found in MG, we suggest that they were buried in the St. Benedict cemetery in spite of the funeral protest ban of 1635. Isotopic data support the various origins of the soldiers as belonging to different army corps from France and Saxony.

Our results suggest residential mobility within the European region for all of the individuals, even the IG individuals who were hypothesized to be of local origin. Prague was a cultural and commercial hub in Central Europe during the 15 th and 16 th centuries (Theinhardt et al., 2005). According to parish registers, people migrated to Prague for personal and professional reasons (Fialová, 2006a;[START_REF] Grulich | Migrace na jihu Čech během 16.-18. století[END_REF]. The Old Town district of Prague accommodated a large number of foreign merchants, particularly in the complex of buildings surrounding the courtyard called the Ungelt, which is located approximately 1 km from St. Benedict. The Ungelt served as a meeting and storage place for traders from Europe and Asia [START_REF] Bělina | Histoire des Pays tchèques[END_REF]Fialová, 2006b). Moreover, houses in the Old Town district of Prague were owned by important political and religious figures from Czech and other European regions, who came to the King's court for different missions with their escorts and staff. When deaths occurred, the bodies were generally buried in the closest neighborhood cemetery [START_REF] Bělina | Histoire des Pays tchèques[END_REF]. Therefore, it is conceivable that the individuals from the IG who were identified as foreign to the Bohemian region could have been merchants or members of the aristocracy originating from Western or Southern Europe. Unfortunately, due to the overlap of environmental isotopic values from dietary and water sources, it is not possible to identify more precisely their places of origin within Europe.

CONCLUSION

The combination of stable isotope analysis, biological data, new 14 Consequently, this mortality may have generated simultaneous burials in the St. Benedict cemetery that is adjacent to the Norbertinum. This paper highlights the importance of stable isotope analysis in early modern studies, as it provides additional independent information to that of historical written sources.

ACKNOWLEDGEMENTS

  δ 13 C values for collagen and carbonate, as well as the δ 15 N values for collagen are used to provide insight into human diet. All the individuals from the St. Benedict cemetery have relatively low δ 13 Ccol values, which is typical of European diets based mostly on C3 plants (e.g., cereals, fruits and vegetables). The relatively high Δ 13 Csc-col (bone) values (> 7‰)

  13 Csc-col (bone) and δ15 Ncol values, such that the MG group has more depleted δ 15 Ncol values and more enriched Δ 13 Csc-col (bone) values than the IG group (Fig.8). Despite this difference, most IG and MG individuals present relatively high δ 15 Ncol values. High δ 15 Ncol values can be explained by either a high reliance on animal proteins or the consumption in smaller quantities of proteins with relatively high δ 15 N values. Unweaned terrestrial herbivores[START_REF] Hedges | Nitrogen isotopes and the trophic level of humans in archaeology[END_REF], herbivores feeding on C3 plants grown on soils fertilized by manure(Boogard et al., 2007;[START_REF] Stevens | Palaeodiet at Eton College Rowing Course, Buckinghamshire: Isotopic changes in human diet in the Neolithic, Bronze Age, Iron Age and Roman periods throughout the British Isles[END_REF] and aquatic resources[START_REF] Vika | Re-investigating fish consumption in Greek antiquity: results from δ 13 C and δ 15 N analysis from fish bone collagen[END_REF] exhibit high δ 15 N values. Although both marine and freshwater resources show high δ 15 N values, freshwater resources have usually lower δ 13 C values

Δ 18

 18 Osc (bone-enamel) absolute values range from 0 to 1.5‰. Large intra-individual variation in δ 18 O values for most individuals from IG and MG1-2-3 indicate that individuals ingested water from different geographical sources throughout their lives, or more precisely between the childhood age and the few last years before the death, and suggest diachronic changes of residence. The δ 18 O values of drinking water (δ 18 Odw) were estimated and compared to the local environmental δ 18 O range for the Bohemian region. We used the equation of Chenery et al. (2012) to derive the δ 18 Odw values from the δ 18 O values in bone and enamel carbonate. The δ 18 Odw values derived from the enamel carbonate range from -7.8 to -5.1‰ (mean = -6.1 ± 0.8‰) for IG and from -10.0‰ to -5.9‰ (mean = -8.1 ± 1.2‰) for MG1-2-3. The δ 18 Odw

  δ 18 Odw value of goat is -7.7‰. The faunal δ 18 Odw values are consistent with the defined local range of environmental δ 18 O values (Fig. 9). With the exception of H62 and H84, all of the individuals from MG1-2-3 have δ 18 Odw values that fall within the range of local δ 18 O values, whereas IG individuals have higher δ 18 Odw values than the local range. Although it is not possible to determine precisely their countries of origin because these regions are not discriminated by their δ 18 O environmental values, the individuals from IG can be identified as foreigners and may be native to Western Europe or the Mediterranean coast (http://www.waterisotopes.org;[START_REF] Bowen | The Online Isotopes in Precipitation Calculator (OIPC), version 2.2[END_REF][START_REF] Bowen | Interpolating the isotopic composition of modern meteoric precipitation[END_REF] (Fig.9). Finally, the range of Δ 18 Osc (bone-enamel) values (from -1.5 to 1.3‰ for IG and from -0.8 to 1.5‰ for MG1-2-3) for IG and MG1-2-3 individuals indicates that these individuals moved across different regions within the Western and Mediterranean part of Europe before they died in Prague.

  C dates and archaeological evidence provides new insight into the role of the St. Benedict cemetery during the fifth occupation phase. Stable isotope analysis reveals differences in diet and drinking water between skeletons buried in MG and IG. Isotopic data also suggest that the majority of the individuals may have spent most of their lives outside of the Bohemian region. The heterogeneity of the St. Benedict population and the distinction between the two grave types are supported by radiocarbon dating and archaeological materials, such as the presence of military buttons. The skeletons found in MG were buried despite the ban on funerals in the St. Benedict cemetery in 1635. The Siege of Prague by the French-Bavarian-Saxon armies (1742) may have caused an epidemic that resulted in the mass mortality of young soldiers.

We thank Dr. Z. Dragoun and Dr. M. Omelka (National Institute of Heritage, Prague), Dr. M. Šmolíková (City of Prague Museum, Prague), Dr. L. Pechacek, D. Čumlivski V. Kovar (National Archiv, Prague) for their permission to conduct sampling on the osteological collection from the St. Benedict cemetery, Dr. M. Balasse for laboratory access, Dr. A. Zazzo for his help in the laboratory and comments on the manuscript and J. Ughetto for his help in the stable isotope measurements (CNRS-MNHN, Paris). The associate editors and the two reviewers are gratefully acknowledged for very helpful suggestions on earlier drafts of this article. This work was supported by La Maison des Sciences de l'Homme d'Aquitaine (Projects 2003-2006 and 2007-2010), by Eco-Net 16368 PB, Barrande 19512 ZF and by the Ministry of Cultural Affairs of the Czech Republic (DKRVO 00023272).


Kevin Salesse
email: ksalesse@ulb.ac.be

Ricardo Fernandes

Xavier De Rochefort

Jaroslav Brůžek

Dominique Castex

Élise Dufour

open-access and collaborative isotope database for bioarchaeological samples from the Graeco-Roman World and its margins Authors

Keywords: 1. Classical Antiquity, 2. Iron age, 3. Diet, 4. Mobility, 5. Paleoenvironments, 6. Georeferenced database, 7. Isotopic proxies

Introduction

Isotopic proxies are widely recognized as a powerful tool to improve knowledge of past human and animal diet and mobility patterns, to ascertain ancient crop and animal management practices, and to reconstruct paleoenvironments (Drucker et al. 2012;[START_REF] Knudson | Migration and Viking Dublin: paleomobility and paleodiet through isotopic analyses[END_REF]Boogard et al. 2013;[START_REF] Müldner | Stable isotopes and diet: their contribution to Romano-British research[END_REF][START_REF] Touzeau | Egyptian mummies record increasing aridity in the Nile valley from 5500 to 1500 yr before present[END_REF][START_REF] Knipper | What is on the menu in a Celtic town? Iron Age diet reconstructed at Basel-Gasfabrik[END_REF][START_REF] De Cupere | Subsistence economy and land use strategies in the Burdur province (SW Anatolia) from prehistory to the Byzantine period[END_REF]. Within archaeological studies isotopic data has allowed for a better understanding of the social structure, political organisation, economy, technology, and environmental contexts of past human groups (e.g. [START_REF] Prowse | Isotopic paleodiet studies of skeletons from the Imperial Roman-age cemetery of Isola Sacra, Rome, Italy[END_REF][START_REF] Craig | Stable isotopic evidence for diet at the imperial Roman coastal site of Velia (1st and 2nd Centuries AD) in southern Italy[END_REF][START_REF] Crowe | Water-related occupations and diet in two Roman coastal communities (Italy, first to third century AD): correlation between stable carbon and nitrogen isotope values and auricular exostosis prevalence[END_REF][START_REF] Pollard | These boots were made for walking": The isotopic analysis of a C4 Roman inhumation from Gravesend, Kent, UK[END_REF][START_REF] Mays | An investigation of diet in early Anglo-Saxon England using carbon and nitrogen stable isotope analysis of human bone collagen[END_REF][START_REF] Salesse | Life history of the individuals buried in the St. Benedict cemetery (Prague, 15 th -18 th Centuries): Insights from 14 C dating and stable isotope (δ 13 C, δ 15 N, δ 18 O) analysis[END_REF][START_REF] Salesse | Variability of bone preservation in a confined environment: The case of the catacomb of Sts Peter and Marcellinus (Rome, Italy)[END_REF][START_REF] Salesse | Archéo-biogéochimie isotopique, reconstitutions des régimes alimentaires et des schémas de mobilité, et interactions bio-culturelles. Les sépultures plurielles de la région X de la catacomb Saints Pierre-et-Marcellin (Rome, I er -III e s. ap[END_REF][START_REF] Killgrove | Diet and collapse: A stable isotope study of Imperial-era Gabii (1 st -3 rd centuries AD)[END_REF]. The number of archaeological publications containing isotopic data has surged during the past 20 years [START_REF] Pestle | Quantifying inter-laboratory variability in stable isotope analysis of ancient skeletal remains[END_REF][START_REF] Szpak | Best practices for calibrating and reporting stable isotope measurements in archaeology[END_REF]. However, the number of isotope web databases remains surprisingly low. There are several databases of radiocarbon data (e.g. RADON, [START_REF] Kneisel | Radon-B[END_REF]CARD, Martindale et al. 2016), databases of modern environmental samples (e.g. IsoMAP, [START_REF] Bowen | IsoMAP: Isoscapes Modeling, Analysis and Prediction (version 1.0)[END_REF]IRHUM, Willmes et al. 2014) or archaeological artefacts (e.g. OXALID, Stos-Gale and Gale 2009). However, only a few databases have gathered bioarchaeological isotope data, and even less include data from human remains (e.g. KIK-IRPA, van Strydonck and de Roock 2011;dIANA, Etu-Shivola et al. 2015;IsoMemo, Fernandes et al. 2017).

With a particular interest in isotopic studies concerning the Greco-Roman world sensu lato, we build IsoArcH, a web isotope database covering a wide chronological range (12 th c. BCE -8 th c. CE) for bioarchaeological samples from European, Middle Eastern and North African contexts. IsoArcH is also a member of the IsoMemo initiative [START_REF] Fernandes | IsoMemo.com: A database of isotopic data for ecology, archaeology, and environmental sciences[END_REF]. The IsoMemo initiative follows a collaborative model for data sharing and project building that brings together different isotope databases within the research fields of ecology, environmental sciences, and archaeology.

IsoArcH is the first and main isotope web database fully dedicated to the Greco-Roman world and its margins. Furthermore, IsoArcH offers unique features, such as data display on ancient world maps, which are not available elsewhere and are of special research interest in the study of the focus region and time period.

Description of IsoArcH

IsoArcH was designed as a web-based isotope database for bioarchaeological samples from Iron Age, Classical Antiquity and Late Antiquity (i.e. 12th c. BCE to 8th c. CE). It is hosted on a server relying entirely on open-source software solutions and implemented following a relational database model. The database structure of IsoArcH is divided according to four different types of bioarchaeological samples: human, animal, plant, and organic residues. Isotopic ratios (δD, δ 13 C, δ 15 N, δ 18 O, δ 34 S and 87 Sr/ 86 Sr) and associated quality control indicators are recorded following two main divisions: organic or mineral fractions on different kinds of samples (e.g. bone, tooth, hair, calculus, etc.). The isotopic data is supplemented by archaeological and chronological information relative to the sample (e.g. identification number, date range, description of archaeological context, etc.). The selection of data fields for supporting information depends on the type of sample. For example, for human samples supporting information includes the description of sex, age at death, stature, and type of burial. Full citation details are provided for collected published data. IsoArcH compiled to this day isotopic data for 4,000+ humans, 2,000+ animals, 100+ plants, and 10+ organic residues from nearly 300 archaeological sites. Detailed information on database organisation and web database architecture is provided in supplementary files 1 and 2.

IsoArcH is a collaborative database accessible to both researchers and the non-academic audience. Users can freely query the database and download the resulting output. Furthermore, users can contribute to expand IsoArcH by uploading complied or their own generated data. IsoArcH administrators check each new submission to ensure the maintenance of data consistency and quality. Once newly submitted data is approved, it is then added to the database and made available online. More information on database collaborative platform is given in supplementary file 3.

As a spatial database dedicated to the Graeco-Roman world and its margins (i.e. Europe, Near and Middle East, and North Africa), all stored isotopic data is georeferenced. Using a web-mapping capability, samples can be framed within the contemporary geopolitical context through their display on ancient world maps. Available ancient world maps include those for the Persian, Alexander's, Roman and Byzantine empires, plus for many other chrono-cultural entities. These maps serve as backgrounds on which archaeological sites are projected (Figure 1). In addition, the projected maps are interactive and can be used to explore the database with or without an initial query. Through the selection of a site, users can have a summary of available data for that site (e.g. site name, number of referenced individuals, population means for isotope values, and references). Detailed information on web-mapping tool architecture is provided in supplementary file 4.

An open-access database policy is followed by IsoArcH which means that data is made available free of restrictions on both access and use. IsoArcH is a public website, accessible at http://www.isoarch.eu, with no login requirement for data visualisation. However, a login is required for database querying and data downloading. The content of IsoArcH is licensed under the Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License (CC BY-NC-SA 4.0). Users are free to copy and redistribute the data from IsoArcH in any medium or format. They can also modify and build upon available data but they must distribute their contributions under the same license as the original. The licensor cannot revoke these freedoms as long as the license terms are followed. Under the previous terms, users must give in their productions 1) appropriate credits (i.e. this publication and "Salesse, K., Fernandes, R., de Rochefort X., Brůžek J., Castex D., Dufour É., (2017), www.isoarch.eu (v.1.0), accessed mm/dd/yyyy"), 2) provide a link to the license (https://creativecommons.org/licenses/by-nc-sa/4.0/), and 3) indicate if any changes were made.

Material obtained from IsoArcH cannot be used for commercial purposes.

The full advantages of the database are expected to arise from its collaborative approach.

IsoArcH plans to become a new efficient tool at the service of the scientific community to provide an overview of the state of paleodiet, paleomobility, and paleoenvironmental research in the ancient Mediterranean. IsoArcH is part of a broadly-based concept of data centralization that should elicit new discussions and encourage stronger interdisciplinary collaboration. The online interface provides easy access to a library of embedded data organized in multiple layers that facilitates the building of local isotopic baselines plus regional and temporal comparisons of data. Finally, IsoArcH will monitor the release of publications pertaining to the Greco-Roman world and collect newly available isotopic data.

Research applications

Isotopic data, together with associated chronological and other supporting information, collected at IsoArcH allows for numerous research applications. These may include large scale comparative studies of human diet or mobility following multiple selection criteria (e.g. chronology, region, social variables). Whereas stored animal isotopic data can contribute to the reconstruction of local environmental and human impact histories. For instance, herbivore collagen carbon or nitrogen stable isotope values can be used as proxies to establish past vegetation types (C 3 or C 4 ), levels of aridity, and forest density [START_REF] Schwarcz | 15N Enrichment in the Sahara: In Search of a Global Relationship[END_REF][START_REF] Kelly | Stable isotopes of carbon and nitrogen in the study of avian and mammalian trophic ecology[END_REF][START_REF] Bonafini | Investigation of the "canopy effect" in the isotope ecology of temperate woodlands[END_REF]. IsoArcH can also be used to identify data gaps for certain regions, time periods, or sample types. Concerning the latter, there is presently a clear insufficiency of published plant isotopic data although this has a great research potential. Carbon and nitrogen stable isotope data for cultivated plants can be used to assess water availability and soil fertility which are also determined by human farming practices such as irrigation and manuring [START_REF] Aguilera | Stable carbon and nitrogen isotopes and quality traits of fossil cereal grains provide clues on sustainability at the beginnings of Mediterranean agriculture[END_REF][START_REF] Szpak | Complexities of nitrogen isotope biogeochemistry in plant-soil systems: implications for the study of ancient agricultural and animal management practices[END_REF][START_REF] Styring | Disentangling the effect of farming practice from aridity on crop stable isotope values: A present-day model from Morocco and its application to early farming sites in the eastern Mediterranean[END_REF]). In addition, both plant and animal isotopic data are required to define temporal and regional baselines for the accurate quantification of human diets in isotope-based studies [START_REF] Fernandes | Quantitative diet reconstruction of a Neolithic population using a Bayesian mixing model (FRUITS): The case study of Ostorf (Germany)[END_REF]. The inter quartile ranges of δ 18 O precip values shown in Figure 2a for the younger and older chronological groups are contained within modern day ranges of δ 18 O precip values observed for the Italian peninsula [START_REF] Lightfoot | On the Use of Biomineral Oxygen Isotope Data to Identify Human Migrants in the Archaeological Record: Intra-Sample Variation, Statistical Methods and Geographical Considerations[END_REF]. However, both chronological groups show a wide range of δ 18 O precip values, larger for the younger group, which is indicative of a high degree of mobility. The δ 18 O precip mean for the younger group (mean δ 18 O precip = -6.8±1.7‰) is slightly smaller than that of the older group (mean δ 18 O precip = -6.3±1.6‰) but the difference is not statistically significant (Welch two sample t-test: t = 1.1863, df = 41.56, p-value = 0.2422). The chronology of the individuals from the younger group roughly coincides with a broadly warmer period (from ca. 250 to 400 CE) for which higher δ 18 O precip values are observed relative to the previous centuries [START_REF] Mccormick | Climate Change during and after the Roman Empire: Reconstructing the Past from Scientific and Historical Evidence[END_REF]. Since the opposite trend is observed for δ 18 O precip values in Figure 2a, it suggests a larger degree of mobility during the second half of the Imperial period which would possibly include a larger proportion of individuals from northern regions. It would be interesting to place this within the context of the 3 rd century crisis and a possibly greater connectivity with the northern regions of the Roman Empire. Nonetheless, some interpretative caution is necessary since the isotopic dataset is limited, both in total numbers and spatial representatively, and the chronological resolution is poor.

Human bone collagen δ 13 C coll and δ 15 N coll signals are proxies for dietary sources of protein [START_REF] Fernandes | A Simple(R) Model to Predict the Source of Dietary Carbon in Individual Consumers[END_REF]. A comparison of these isotopic signals is shown in Figure 2b for Romano-British adult male and female individuals. The difference between male (mean δ 13 C coll = -19.5±0.7‰) and female (mean δ 13 C coll = -19.6±0.6 ‰) mean δ 13 C coll values is small and not statistically significant (Welch two sample t-test: t = 1.6429, df = 319.89, p-value = 0.1014). There is a larger difference between male (mean δ 15 N coll = 10.4±1.2‰) and female (mean δ 15 N coll = 9.5±1.3‰) mean δ 15 N coll values that is statistically significant (Welch two sample t-test: t = 4.785, df = 269.89, p-value = 2.818e-06). The difference in δ 15 N coll values is likely due to a higher consumption by men of terrestrial domesticated animal protein having δ 15 N values higher than plant protein. Differentiated consumption of marine fish protein, having elevated δ 15 N and δ 13 C values compared to terrestrial protein sources, is unlikely given the similarity in δ 13 C coll values for both genders. The energetic cost of producing animal protein is greater than that of plant protein making access to animal protein typically more limited. This could imply that men had a higher social status than women, although other hypotheses for observed isotopic gender differences have also been previously put forward [START_REF] Craig | Stable isotopic evidence for diet at the imperial Roman coastal site of Velia (1st and 2nd Centuries AD) in southern Italy[END_REF]. Furthermore, possible differences in social status were certainly not only genderbased as females show a larger variability in δ 15 N coll values compared to men.

The impact of regional climatic and environmental variability in herbivore bone collagen δ 13 C coll and δ 15 N coll signals is illustrated in Figure 2c through a comparison of Roman herbivore data from the United Kingdom, Italy, and Egypt. There are large differences in the number of available records for the three regions with Egypt represented by a single location (Kellis). However, large isotopic differences can be observed between Egypt and European regions. Higher Egyptian herbivore δ 15 N coll values reflect higher plant δ 15 N values resulting from lower levels of precipitation in Egypt compared to European regions [START_REF] Schwarcz | 15N Enrichment in the Sahara: In Search of a Global Relationship[END_REF]. The more arid environment of Egypt also results in a larger abundance of C 4 plants which are better adapted than C 3 plants to such environments and have more elevated δ 13 C values (Tiezen 1991). There is a statistically significant difference between the δ 13 C coll values of British and Italian samples (Welch two sample t-test: t = -2.5301, df = 21.885, p-value = 0.01911). Herbivores from Roman Italy have a larger mean δ 13 C coll value (mean δ 13 C coll = -21.1±1.0‰), and also a larger amount of variability, compared to Romano-British herbivores (mean δ 13 C coll = -21.6±0.5‰). Plant δ 13 C values decrease with higher mean annual precipitation and higher forest density (canopy effect) [START_REF] Aguilera | Stable carbon and nitrogen isotopes and quality traits of fossil cereal grains provide clues on sustainability at the beginnings of Mediterranean agriculture[END_REF][START_REF] Bonafini | Investigation of the "canopy effect" in the isotope ecology of temperate woodlands[END_REF]).

Both of these parameters have, in general, higher values in Britain than in Italy. There was also a statistically significant difference between δ 15 N coll values from British and Italian samples (Welch two sample t-test: t = 2.7093, df = 22.67, p-value = 0.01261). Romano-British herbivores have a larger mean δ 15 N coll value (mean δ 15 N coll = 5.3±1.7‰) compared to herbivores from Roman Italy (mean δ 15 N coll = 4.3±1.7‰). This suggests that British soils accessible to local herbivores were more fertile than Italian soils and that Italian herbivores did not have a significant access to manured fields [START_REF] Aguilera | Stable carbon and nitrogen isotopes and quality traits of fossil cereal grains provide clues on sustainability at the beginnings of Mediterranean agriculture[END_REF][START_REF] Szpak | Complexities of nitrogen isotope biogeochemistry in plant-soil systems: implications for the study of ancient agricultural and animal management practices[END_REF].

One of the significant repercussions of observed animal isotopic variability across different regions is the need to establish a local and contemporary isotopic baseline when doing isotope-based human diet reconstruction. This is illustrated through a simple example in which the diet of Roman adult individuals from the Egyptian site of Kellis was quantitatively reconstructed from published tooth (M3 molar) dentin isotopic data (mean δ 13 C coll = -18.8±0.3‰ and mean δ 15 N coll = 17.7±1.0‰) using the Bayesian mixing model FRUITS [START_REF] Dupras | Reconstructing infant weaning histories at Roman period Kellis, Egypt using stable isotope analysis of dentition[END_REF][START_REF] Fernandes | Food Reconstruction Using Isotopic Transferred Signals (FRUITS): a Bayesian model for diet reconstruction[END_REF]. The adopted modelling approach is essentially the same as employed for individuals from the Roman city of Herculaneum (Italy) in which protein contributions (marine vs. terrestrial) were quantified [START_REF] Fernandes | A Simple(R) Model to Predict the Source of Dietary Carbon in Individual Consumers[END_REF]. The accuracy of model estimates for the Herculaneum individuals was assessed by comparing individual model estimates with observed human dietary radiocarbon reservoir effects showing an excellent agreement. Two isotopic baselines were considered to estimate the group protein contributions for the adults from Kellis. One relying on Italian herbivore isotopic data as described in [START_REF] Fernandes | A Simple(R) Model to Predict the Source of Dietary Carbon in Individual Consumers[END_REF] and a second relying on Egyptian herbivore isotopic data as shown in Figure 2c. For both baselines the same isotopic values of Mediterranean marine fish were taken as reference. Model estimates are shown in Figure 3 and demonstrate the differences in protein estimates generated under the two isotopic baselines. Also included in Figure 3 is the estimated group protein contribution for adults from Herculaneum (filled circles). Estimates generated using an Egyptian isotopic baseline result in similar group dietary estimates for Kellis and Herculaneum adults.

Conclusions and future developments

The few research examples shown in this paper illustrated how data stored at IsoArcH allows for multi-scale analysis and extensive studies on topics related to paleodiet, paleomobility and paleoenvironment. The task of defining contemporary and local baselines necessary for the study of subsistence strategies and mobility patterns of past humans and animals becomes greatly simplified.

Database querying also highlights existing data gaps for certain sample types, time periods, and regions which motivate future isotopic research.

IsoArcH database will be expanded in the future by adding new data and entities (e.g. additional isotopic proxies, new archaeological parameters, etc.). This will follow from the feedback provided by the users of IsoArcH. A forum addressed to researchers using the website is envisaged for discussions on IsoArcH related topics. Tutorials, possibly in the form of a video, will be available on the website to describe to users how to use IsoArcH. We also plan to implement free statistical tools online (e.g. Shiny, a web application framework for R) as well as implement the capability to export the ancient world maps generated on IsoArcH. Automatic submission tools are planned to be developed so that batch data submissions might become easier. Moreover, user session will be expanded to allow members to operate IsoArcH using their own unpublished works and make use of online tools (e.g. digital maps, datasets, baselines) without being compelled to share their data publicly.

Figure 1 .

 1 Figure 1. Example of a map generated through IsoArcH showing the distribution of Roman archaeological sites where isotopic data from human and non-humans samples are available. The used map overlay is available from DARMC and shows the Roman provinces between 303 and 324 CE.

  Within this section a few illustrative examples are given and briefly discussed to demonstrate research uses for the data made available at IsoArcH. Oxygen isotopes measured in human teeth and bone chiefly reflect the isotopic composition of drinking water and have been frequently used in Roman mobility studies (see Killgrove & Montgomery 2016 and references therein). A simple temporal comparison was made of human oxygen isotopic data from the Italian peninsula. Selected for comparison was tooth δ 18 O data (a single tooth per individual, mostly third molars) from human remains dating between 400 BCE and 400 CE. The selection was further limited to individuals for which the difference between the upper and lower limit of the assigned chronological boundaries was lower than 200 years. The individuals were grouped into two broad chronological groups (<~ 200CE and ≥ ~200 CE) using as criterion the median of the chronological boundaries assigned to each individual. Different types or reported measurements and units of reported δ 18 O tooth data (δ 18 O carbonate or phosphate relative to VPDB or VSMOW standards) were subjected to necessary calculations to report these as δ 18 O precipitation values relative to the VSMOW standard(Chenery et al.2012). Boxplots for selected human data δ 18 O precip are shown in Figure2a.

Figure 2

 2 Figure 2. a) Comparison of δ 18 O precip values calculated from tooth δ 18 O data for Roman individuals from the Italian peninsula. b) Comparison of Romano-British male and female human bone collagen δ 13 C coll (b1) and δ 15 N coll (b2) values. c) Comparison of Roman British, Italian, and Egyptian herbivore bone collagen δ 13 C coll (c1) and δ 15 N coll (c2) values. Box edges represent 25 th and 75 th percentiles (inter quartile range or IQR) while the horizontal line is the 50 th percentile (median). Whiskers are the minimum and maximum values that do not exceed a distance of 1.5 times the IQR. Beyond this distance single points represent outliers.

Figure 3 .

 3 Figure 3. Comparison of dietary protein Bayesian group estimates for adults from Kellis under two isotopic baselines (Italian and Egyptian). Filled circles represent estimated mean protein contribution for Herculaneum group boxes represent a 68% credible interval while the whiskers represent a 95% credible interval. The horizontal continuous line indicates the average while the horizontal discontinuous line indicates the median.

Acknowledgements

We would like to thank Dr. Arwa Kharobi for her help and her constructive criticism on IsoArcH.

We wish to express his special gratitude to Mr. Romain Leguay, Mr. Nicolas Filippi as well as Ms. Mi Wu for their technical counsel and assistance with IT tasks. In addition, Ms. Christine Bergmann and M. Aurélien Tafani are thanked for the English editing of this paper and the website. Dr Kevin Salesse would like to express his gratitude to Dr. Martine Vercauteren for hosting in her research unit of Anthropology and Human genetics at the Université Libre de Bruxelles in Belgium. Data gathering has been mainly carried out by Dr Kevin Salesse during his PhD (Université de Bordeaux, Pessac; Muséum national d'Histoire naturelle, Paris) and post-doctoral positions (University of South Florida, Tampa). He was financed by a scholarship of the Ministère de l'Enseignement Supérieur et de la Recherche (2010-2015) as well as the Shohet Scholars Program of the International Catacomb Society (2015-2016). The development of the web database and the website was performed in parallel to his main research activities and was totally self-financed.