text: Twigstats substantially improves models of admixture between 
  ancestries from Iron Age Britain and northern Europe in early medi- 
  eval England9, halving standard errors from 9% with SNPs to 4% when 
  using time stratification (point estimates 80% and 79% Iron Age 
  Britain-related ancestry, respectively). We used this improved reso- 
  lution to demonstrate that an earlier Roman individual (6DT3) dating 
  to approximately second to fourth century ce from the purported 
  gladiator or military cemetery at Driffield Terrace in York (Roman 
  *Eboracum*), England60, who was previously identified as an ancestry 
  outlier61,62, specifically carried approximately 25% EIA Scandinavian 
  Peninsula-related ancestry (Fig. 2c). This documents that people with 
  Scandinavian-related ancestry already were in Britain before the fifth 
  century ce, after which there was a substantial influx associated with 
  Anglo-Saxon migrations9. Although it is uncertain whether this indi- 
  vidual was a gladiator or soldier, individuals and groups from northern 
  Europe are indeed recorded in Roman sources both as soldiers and as 
  enslaved gladiators63,64. 
  
  Across Europe, we see regional differences in the southeastern and 
  southwestern expansions of Scandinavian-related ancestries. Early 
  medieval groups from present-day Poland and Slovakia carry spe- 
  cific ancestry from one of the Scandinavian EIA groups—the one with 
  individuals primarily from the northern parts of Scandinavia in the 
  EIA—with no evidence of ancestry related to the other primary group 
  in more southern Scandinavia (Fig. 2d). By contrast, in southern and 
  western Europe, Scandinavian-related ancestry either derives from 