text: Ancient genome sequencing has revolutionized our ability to recon- 
  struct expansions, migrations and admixture events in the ancient past 
  and understand their impact on human genetic variation today. How- 
  ever, tracing history using genetic ancestry has remained challenging, 
  particularly in historical periods for which the richest comparative 
  information from history and archaeology often exists. This is because 
  ancestries in many geographical regions are often so similar as to be 
  statistically indistinguishable with current approaches. One example is 
  northern and central Europe since the start of the Iron Age around 500 
  bce, a period for which many long-standing questions remain, such as 
  the nature of large-scale patterns of human migration during the fourth 
  to sixth centuries ce, their impact on the Mediterranean world and later 
  patterns of human mobility during the Viking Age (around 750–1050 ce). 
  Several recent studies have documented substantial mobility and 
  genetic diversity in these time periods, suggesting stable population 
  structure despite high mobility5, and have revealed genetic variation 
  in Viking Age Scandinavia6–8, early medieval England3,9, early medieval 
  Hungary10,11 and Iron Age and medieval Poland12. However, previous 
  studies mostly used large modern cohorts to study ancestry change 
  through time and space. This is because the differentiation between 
  Iron Age groups in central and northern Europe is an order of magnitude 
  lower (fixation index (*F*ST) = 0.1–0.7%; Extended Data Fig. 1) than, for 
  example, the more commonly studied hunter-gatherer, early farmer 
  and steppe-pastoralist groups that shaped the ancestry landscape of 