The shifting dynamics of ancestry and culture at a post-Roman crossroads

The collapse of the western Roman Empire in the 5th century created a period of geopolitical upheaval, driven by Barbarians dispersing into the former Empire and reshaping post-Roman communities. While there is now evidence for a major genetic impact of these migrations into specific regions of Europe, it is unknown whether these changes in ancestry were uniform across the continent. We investigate present-day Slovenia, a crucial crossroad connecting the Roman East and West and the gate to Italy during the Langobard invasion. We conducted paleogenomic and isotopic analyses of 410 individuals from 21 sites across Slovenia and Cividale (Italy), establishing a longitudinal transect, spanning eight centuries. During Late Antiquity, despite changes in burial artifacts, kinship practices, and settlement structures reflecting a shift in culture, we find high levels of genetic continuity with the local Late Roman population and reduced mobility. However, demographic turnover began during the 8th century, when communities with northeastern European ancestry and distinct cultural practices entered the region, gradually advancing westward over the span of three centuries, replacing the local populations. This shows that cultural change in post-Roman Europe could be decoupled from genetic change in transit zones, demonstrating a dynamic spatiotemporal process across the continent.