Isotopic evidence for changing human mobility patterns after the disintegration of the Western Roman Empire at the Upper Rhine

The dissolution of the Western Roman Empire and the rise of Early Medieval kingdoms during the fifth and sixth century AD were accompanied by profound social, economic, and cultural changes. While several studies focus on the investigation of the reasons explaining the underlying cause of this transition based on written and archeological evidence, it is still unclear in how far this major political turnover affected communities on a regional and local level. Here, we conduct strontium, oxygen, and carbon isotope analyses of human tooth enamel from 95 individuals from two Early Medieval cemeteries located in the northern Upper Rhine region in order to investigate population dynamics during a period of political upheaval. The strontium isotopic analysis has revealed that a high number of individuals born outside the Upper Rhine region, but relative few individuals indigenous to the area, were interred in cemeteries newly founded at the end of the fifth century AD. During the sixth century AD, the cemeteries are dominated by individuals local to the Upper Rhine region. However, the presence of individuals with strontium isotope values below the biologically available strontium isotopic range indicates the arrival of newcomers from different regions compared to earlier periods which may reflect a change of contacts and relationships in the course of the sixth century AD. Overall, the results of this study suggest that the change of human mobility patterns in this region is a reaction to the socio-political dynamics of the transformation period between Late Antiquity and the Early Middle Ages.