The twelfth century witnessed the emergence of a new form of Catholic religious life, the military orders, whose members have commonly been referred to as "warrior monks." This misleading term has caused confusion and controversy regarding the orders' identity. They were more deeply rooted in nascent European chivalry and crusading spirituality than in the monastic tradition; the structures and vows of religious life guaranteed their institutional stability and commitment to crusading ideals. This military-religious ethos is best described as "ecclesiastical chivalry," as it drew the knightly brethren away from secular chivalry's cultural milieu towards the traditions and prerogatives of the hierarchical Church. First emerging in the Latin East, the military orders quickly spread to other crusading theaters, most notably the Iberian Peninsula. The Orders of Santiago, Calatrava and Alcántara, headquartered in the Kingdoms of Leon and Castile, were distinct Iberian permutations of ecclesiastical chivalry that both imitated existing models and adapted themselves to local circumstances. This study sketches an outline of their distinct vocation through an examination of their historical and spiritual foundations, religious observance, mission and purpose in the world, and relations with one another. Over the course of the late thirteenth and early fourteenth centuries, the Iberian military orders underwent change and decline that transformed their distinct way of life, bringing it closer to the late medieval pattern of lay Christian chivalry.