Contrasting demographic impacts of Roman colonization and early medieval migrations in the Iberian Peninsula.

It has been unclear how Roman and later Germanic political control shaped the demography of Iberia and how it differed from other parts of Europe. We report genetic data from 243 ancient individuals dating to 100-800 CE, analyzed alongside 58 previously published individuals. In Roman times, we document an influx of people with ancestry from the Eastern Mediterranean and an influx of North Africans, especially in the center and south. Beginning in the 5th century, Germanic and Alan (Sarmatian) groups assumed political control. Although we identify individuals with Central-Northern European-associated ancestry, including siblings buried ∼725 km apart, the Hispano-Roman population remained continuous in Iberia. These demographic patterns contrast sharply with those in Britain, where major demographic change followed Rome's collapse, and with those in the central Mediterranean, where both periods were associated with profound transformations. Together, these findings highlight regional variation in admixture and continuity across post-Roman Europe.