Lucas, the garrulous bishop of Tuy, included the thaumaturgy of Saint Dominic of Silos as one of the glories of Spain in his mid-thirteenth-century account of the Peninsula's history. This study examines the rise to prominence of one of the most important of saints' cults in Medieval Spain and its development throughout the Middle Ages. It interrogates neglected texts such as the late eleventh-century Vita Dominici Exiliensis and the late thirteenth-century Miraculos romancados (as well as artistic representations and works written outside Silos), and places the more widely known Vida de Santo Domingo by Gonzalo de Berceo (c. 1260) in a new light by firmly fixing its presentation of the saint within the development of the cult. Dominic's veneration became centred upon his role in freeing captives, and a study of this phenomenon provides a focus on the frontier and its settlers through their devotion to the saint, as well as illuminating their view of their Muslim adversaries. This is not the only centre of interest in the book, and a variety of approaches are employed to draw as round a picture as possible of the functioning of this saint's cult, from analysis of the manuscript traditions of the various works discussed to a consideration of the anthropology of Silos as a pilgrimage centre. All quotations are given in both Latin or Romance with an English translation.