The church, Iglesia del Sagrario, is built on the site where the city's great mosque once stood. If you stand beneath the central cupola you can take in the exact symmetry of the ceiling. Buried in a side chapel is one of the heroes of the Reconquista, Hernán Pérez del Pulgar: he slipped into the city while it was still occupied by the Arabs and nailed to the door of the mosque a parchment bearing the words "Ave María" and declaring that the mosque had been seized by Christendom.