Differing Demographic Impacts of Roman Colonization and Early Medieval Migrations in the Iberian Peninsula

Abstract

Roman and later Germanic rule deeply shaped the population history of the Iberian Peninsula. We present genome-wide data from 259 ancient individuals dating to 100–800 CE, co-analyzed with 58 previously published individuals. During the Roman period, Iberia underwent major demographic change, marked by substantial influxes of ancestry from the Eastern Mediterranean across all regions, and from North Africa particularly in central and southern Iberia. In contrast, the Migration Period introduced more limited genetic input: while individuals with Central-North European ancestry, linked to Suebi, Vandals, Visigoths, and Alans, are found at sites with Germanic-style ornaments (sometimes showing long-distance kinship, such as siblings buried 725 km apart) the broader population remained largely continuous with the preceding Hispano-Roman gene pool. Iberia’s demographic trajectory thus diverges from Britain, where changes were delayed until the Migration Period, and from the central Mediterranean, where both phases brought major transformations, highlighting region-specific dynamics of empire and migration.