This volume examines the nature of aristocratic society in the Spanish kingdom of León and Castile in the twelfth century. Drawing on an extensive range of original sources, many of them unpublished, it highlights the unrivalled wealth, status and power enjoyed by some members of the aristocracy. It also explores the multifarious roles that lay magnates were expected to fulfil: as family protectors, landlords and judges; as courtiers, diplomats and military commanders; and, not least, as patrons of the church. The nobility of León and Castile experienced a number of important changes during this period. There are signs that a few great families began to develop an embryonic sense of lineage. The struggle for ascendancy with al-Andalus - Muslim Spain - also enabled some magnates to acquire influence far from their traditional centres of power, and the concept of crusade made itself felt in aristocratic circles. The book’s Appendices include a unique biographical study of the counts of León and Castile and a selection of genealogical tables.