The genealogies in “The Book of Settlements” (Landnámabók) do not represent complete genealogies of medieval Icelanders, but rather only those branches that were relevant to the compilers’ purposes. Moreover, the names of some original settlers may have been lost, while others (who did not actually exist) were retrospectively “reconstructed” from place names. In this regard, sections of the Landnámabók that mention three brothers are particularly noteworthy. At first glance, this could reflect the reality of large families in medieval Iceland. However, in cases involving three sons, they are not simply mentioned in genealogical lists but are introduced with the formulaic phrase þau áttu þrjá sonu (“they had three sons”), emphasising their renown and the large number of their descendants. While these accounts may contain echoes of historical events, they could also be a product of oral transmission, where formulaic phrases and triadic structures facilitated the preservation and transmission of narratives. The widespread folkloric motif of the “three brothers” could have influenced the nature of the information transmitted by the oral tradition, and the “extra” brothers could be forgotten, or a third brother could be added to an original pair.