## 2 Material and Methods
### Methods  
The isotopic analysis was conducted at the Stable Isotope and Radiocarbon Unit of the Institute of Nanoscience and Nanotechnology, of N.C.S.R. Demokritos, in Athens, Greece. Collagen was extracted from the bone samples following the experimental process in [67; 68]. About 250 mg of bone sample was crushed into small chunks after being treated with an ultrasound. These small pieces were immersed in 0.5 M hydrochloric acid (HCI) until the minerals were broken down. The remaining pieces were rinsed with distilled water and then immersed in 0.5 M sodium hydroxide (NaOH) for 20 h in order to remove the humic contaminants. The chunks were again rinsed with distilled water and then immersed in an aqueous solution that reached 100 \({}^{\circ}\)C, until the isolation of collagen was feasible. The collagen was treated by a lyophilization process (freeze-dried). The good preservation of collagen was verified by the atomic C:N ratio, which should be between 2.9 and 3.6 [10], and by collagen yields, which should be over 1 wt % [69].  
For the apatite extraction, we followed the protocol of [PERSON] et al. (1996) [70] with a modification by [PERSON] et al. (2011) [71]. The bones were powdered and treated in NaOCl (2-3%) for 24 h on a rotator at room temperature in order to oxidize the organic residues. Afterwards, they were rinsed with distilled water and soaked in an acetic acid-Ca acetate buffer (1M) for 24 h on a rotator at room temperature in order to remove the exogenous carbonate.  
Figure 1: List graves in EIA Cemetery of Agras.  
The isotopic ratios are expressed for carbon as \(\delta^{13}\)C versus marine carbonate (PDB), for nitrogen as \(\delta^{15}\)N versus atmospheric N\({}_{2}\) (AIR), and for \(\delta^{18}\)O of apatite versus PDB. The \(\delta^{18}\)O of water samples was measured versus the Vienna Standard Mean Ocean Water (VSMOW).  
We use the \(\delta\) notation:  
\[\delta=(\text{R}_{\text{sample}}-\text{R}_{\text{standard}})/\text{R}_{\text{ standard}}]\times 1000,\]  
with R either \({}^{13}\)C/\({}^{12}\)C or \({}^{15}\)N/\({}^{14}\)N or \({}^{18}\)O/\({}^{16}\)O. The measurement precision was 0.1% for measured isotopes.  
The values of \(\delta^{13}\)C and \(\delta^{15}\)N for contemporary hair samples collected in Alexandreia were corrected by 1.41% and 0.86%, respectively, in order to correspond to the bone collagen values [72]. The corresponding bone collagen values \(\delta^{13}\)C values for Alexandreia [2] were corrected by the Suess Effect [73] (we added 1.5% to the \(\delta^{13}\)C values of the contemporary samples) in order to compare them with the archaeological results. Finally, for three of our samples we performed Accelerator Mass Spectrometry / Radiocarbon dating. Calibration was performed with the most recent curve data for the northern hemisphere [74].  
Radiocarbon aging determinations were performed using the Liquid Scintillation Counting method (LSC) [75].  
In order to determine the contribution percentages of each source in the diet, a set of mass balance equations using the stable isotope values was solved with the Bayesian statistical packages IsoSource [76] and FRUITS [77].