Disparate demographic impacts of the Roman Colonization and the Migration Period in the Iberian Peninsula.

It has been unclear how the periods of Roman and later Germanic political control shaped the demography of the Iberian Peninsula and how Iberia differs in these respects from other parts of the Roman Empire. We report genome-wide data from 248 ancient individuals from the largely unsampled period 100-800 CE and co-analyze them with previously reported data. In the Roman era, we document profound demographic transformation, with an influx of people with ancestry from the Central and Eastern Mediterranean in all the areas under study and of North Africans, especially in central and southern Iberia. Germanic (Buri, Suebi, Vandals & Visigoths) and Sarmatian (Alans) took over political control beginning in the 5th century, and although we identify individuals with Germanic-associated ancestry at sites with Germanic-style ornaments and observe that such individuals were closely related across large distances as in the case of two siblings separated by 700 km, for Iberia as a whole, we observe high continuity with the previous Hispano-Roman population. The demographic patterns in Iberia contrast sharply with those in Britain, which showed the opposite pattern of little change in the Roman period followed by great change in the Migration period, and also from demographic patterns in the central Mediterranean where both periods were associated with profound transformation, raising broader questions about the forces that precipitated change over this time.