Tracing residential mobility during the Merovingian period: An isotopic analysis of human remains from the Upper Rhine Valley, Germany

Objectives: Written sources have provided information about the rise of Merovingian power and their territorial conquests after the disintegration of the Western Roman Empire, but the extent to which altered power relations in the newly annexed territories reshaped regional and local communities is poorly understood. The early medieval cemetery of Dirmstein, located in the Upper Rhine Valley, is one of the rare sites bearing archeological evidence of simultaneous use by an indigenous community and newcomers from outside the Merovingian core area, and it offers the opportunity to investigate residential mobility at the former Roman Rhine frontier during the Merovingian period. Materials and Methods: We conducted strontium, oxygen, and carbon isotope analyses on human tooth enamel recovered from 25 sixth century inhumations at the Dirmstein cemetery to establish the presence of newcomers to the Upper Rhine region. Results: The low δ¹³C values exhibited by the Dirmstein individuals revealed ingestion of a C₃ terrestrial based diet, with no detectable contribution of C₄ plants, which indicates the absence of individuals from regions where a C₄-based diet was common. Human ⁸⁷Sr/⁸⁶Sr values well outside the local range of bioavailable strontium, in combination with low δ¹⁸O values, suggest a notable presence of newcomers from more eastern or high altitude regions. Conclusions: The isotopic evidence indicates that residential mobility was important and new settlers, most likely from outside the Merovingian core area, contributed to the settlement of the northern Upper Rhine Valley during the sixth century AD.