Our genomic analyses shed light on long-standing questions raised by historical sources and archaeological evidence from the Viking Age. We largely confirm the long-argued movements of Vikings outside Scandinavia: Vikings from present-day Denmark, Norway, and Sweden going to Britain, the islands of the North Atlantic, and sailing east towards the Baltic region and beyond, respectively. However, we also see ancient Swedish-like and Finnish-like ancestry in the westernmost fringes of Europe, and Danish-like ancestry in the east, defying modern historical groupings. It is likely that many such individuals were from communities with mixed ancestries, thrown together by complex trading, raiding and settling networks that crossed cultures and the continent.
During the Viking Age, different parts of Scandinavia were not evenly connected, leading to clear genetic structure in the region. Scandinavia probably comprised a limited number of transport zones and maritime enclaves46 with active external contacts, and limited external gene flow into the rest of the Scandinavian landmass. Some Viking Age Scandinavian locations are relatively homogeneous—particularly mid-Norway, Jutland and the Atlantic settlements. This contrasts with the strong genetic variation of populous coastal and southern trading communities such as in the islands of Gotland and Öland47,48,49. The high genetic heterogeneity in coastal communities implies increased population size, extending a previously proposed10 urbanization model for the Late Viking Age city of Sigtuna (which suggested that more-cosmopolitan trading centres were already present at the end of the Viking Age in Northern Europe) both spatially and further back in time. The formation of large-scale trading and cultural networks that spread people, goods and warfare took time to affect the heartlands of Scandinavia, which retained pre-existing genetic differences into the Medieval period.
Finally, our findings show that Vikings were not simply a direct continuation of Scandinavian Iron Age groups. Instead, we observe gene flow from the south and east into Scandinavia, starting in the Iron Age and continuing throughout the duration of the Viking Age, from an increasing number of sources. Many Viking Age individuals—both within and outside Scandinavia—have high levels of non-Scandinavian ancestry, which suggests ongoing gene flow across Europe.