The church of San Miguel of Almazán (Soria, Spain) houses a twelfth-century antependium ornamented with scenes of Thomas Becket’s martyrdom. Discovered during restoration works in 1936, its origin and its original location are unknown. The aim of this article is twofold—to frame its manufacture chronologically in light of recent research on late-Romanesque sculpture in Castile, and to use this information to discover who commissioned this work: The bishops of Sigüenza, whose diocese included Almazán? The canons of the monastery of Allende Duero built at the foot of Almazán’s town wall? Or, as has always been claimed, the Castilian Monarchs Alfonso VIII and Eleanor of England, who were the chief promoters of the Becket cult in their dominions? Whatever the answer, this relief is one of the earliest examples of Canterbury saint iconography in the Crown of Castile.