Unveiling the complexity of post-Roman polity formation in Pannonia using ancient DNA

Abstract

INTRODUCTION With the decline of the Western Roman Empire, the fourth to sixth centuries common era (CE) were a period of profound demographic, cultural, and political change on the European continent. Although these changes have traditionally been attributed to the migration of “barbarians,” modern scholars have tended to emphasize the role of internal social dynamics. However, the lack of contemporaneous written records has limited what we can say about post-Roman communities. The combined analysis of ancient DNA, isotopes, and the archaeological record from these ancient communities provides another dimension to help us understand the period. RATIONALE The Little Hungarian Plain was part of the Pannonian provinces of the Roman Empire and was an important frontier zone, and its rich archaeological record provides an ideal case study for using ancient DNA to better understand these transformations. Therefore, we sequenced 314 ancient genomes dated between the third and sixth centuries CE from seven (two late Roman and five post-Roman) cemeteries. We then integrated these data with isotopic and archaeological evidence to provide a high-resolution picture of migration and community development in the region. RESULTS We found that the genetic profile of the populations changed substantially in the post-Roman period, with a major influx of Northern European genetic ancestry. This likely reflects the historically documented expansion of the Langobards into the region, although this immigrant population appears to have mixed with the existing local late Roman inhabitants rather than replacing them. In addition, although individual post-Roman cemeteries had highly similar genomic profiles, they demonstrated a variety of patterns of within- and between-cemetery biological relatedness. CONCLUSION Rather than representing simple, independent rural communities, our data revealed a complex, stratified society. By combining genetic and archaeological data at an unprecedented spatial and temporal scale, we were able to identify distinct social hierarchies in which core kin groups likely maintained political and social power. This suggests that the formation of the post-Roman Langobard polity was driven by the establishment of these hierarchical networks, connecting communities on cultural, political, and biological levels.