A triple isotope approach (Sr-O-C) to assess human mobility dynamics in the Lower Germanic limes borderscape (40–470 CE)

The intention of the Roman administration to develop the Lower Germanic limes region into a military zone must have been a catalyst for (long-distance) human and faunal mobility in the course of the 1st century CE. A triple isotope approach (Sr-O-C) has been used on a total of 21 cremations (bone and pars petrosa) and 21 inhumations (dental elements) from the Dutch Lower Germanic limes borderscape region to study the demographic dynamics between 150 and 500 CE. The dental enamel 87Sr/86Sr range from 0.7086 to 0.7158. The variability in Sr within the cremated remains is more limited: 0.7089 to 0.7103. The δ18OPDB data range from −7.6 ‰ to −4.3 ‰. All but one individual dating to the Early and Middle Roman period exhibit Sr ratios that are consistent with the expected local (0.7088–0.7092) or regional (up to ± 0.7110) 87Sr/86Sr signature. The population dynamics drastically change in the subsequent Late Roman period. Fifty percent (6/12) of the investigated Late Roman population (partially) spent part of their childhood away from the Dutch river system or even the Batavian civitas. The cremated long bone 87Sr/86Sr possibly point towards residential stability during the last few years of life: all data are compatible with the expected regional Sr signature. The δ13CPDB data vary between −16.0 ‰ and −8.7 ‰: the latter was indicative of a diet rich in C4 food, which was not a staple in the Roman diet in the Lower Germanic limes region. Although more research is essential to better understand the population dynamics in the limes borderscape, it is clear that the isotope data reflect the political-military status of the Lower Germanic limes region, especially during the transition to a militarized zone in the later Roman period. Identifying possible regions of provenance is a challenge. Another proxy for provenance, namely the cultural artefacts associated with the excavated people, did not show a specific relationship between cultural background and geographical origin