For much of the Middle Ages, the Lara family was among the most powerful aristocratic lineages in Spain. Proteges of the monarchy at the time of El Cid, their influence reached extraordinary heights during the struggle against the Moors. Hand-in-glove with successive kings, they gathered an impressive array of military and political positions across the Iberian Peninsula. But cooperation gave way to confrontation, as the family was pitted against the crown in a series of civil wars.

This book, the first modern study of the Laras, explores the causes of change in the dynamics of...