Variability along the Frontier: Stable carbon and nitrogen isotope ratio analysis of human remains from the Late Roman-Early Byzantine cemetery site of Joan Planells, Ibiza, Spain

Carbon (δ13C) and nitrogen (δ15N) stable isotope analysis of human bone collagen from 38 individuals was undertaken to assess diet at the Late Roman–Early Byzantine (AD 300–700) cemetery site, Joan Planells, in Ibiza, Spain. The results (δ13C = − 18.7 ± 0.5‰ and δ15N = 10.1 ± 1.3‰) show that the diet of this population was derived predominantly from C3 terrestrial resources; plant foods were likely dietary staples along with meat and/or dairy produce comprising an important component of diet. Variation in stable isotope ratio values suggests individual differences in diet. Two individuals, both males, are statistical outliers with distinctive δ15N values (14.4 and 14.8‰) that point to significant consumption of marine resources. Females, on average, have higher δ13C values than males. The parsimonious explanation for this observation is the greater inclusion of C4 resources such as millet in the diets of females. Comparison of the diet of the Joan Planells population with other Late Roman period sites on the Hispanic mainland and other parts of the Mediterranean region suggests that populations may have been responding to a combination of socio-political and environmental factors that could have included Roman influence of food consumptive practices in some of these distant locales.