This article deals with representations of Christian-Islamic confluence in the medieval Portuguese genealogical compilation known as Livro de Linhagens do Conde D. Pedro (Count Pedro’s Book of Lineages), assembled in the mid-fourteenth century by Count Pedro of Barcelos. Several narratives dealing with the non-military interaction of Christians and Muslims are analysed in this article, which discusses their role in the aristocratic discourses of political legitimization. The article’s main argument is that, when evoking ancestors who reinforced the family’s prestige, medieval Portuguese aristocratic families considered ethnic and cultural origin as secondary to their ancestors’ social status.