Constructed on a simple hypostyle plan, ‛Abd al-Rahman's mosque of 785 consisted of 11 aisles of 12 bays that, like the Great Mosque at Damascus, ran perpendicular to a walled court. Each bay was defined by a set of two-tiered horseshoe arches with alternating red brick and white stone voussoirs, which were later coloured. It was enlarged by building programs until 988. In 1236 Ferdinand III of Castile and a number of bishops purified the Great Mosque for Christian worship, consecrating it as a cathedral dedicated to S María. The building was initially altered only by the creation of St. Clement's Chapel and by a number of Christian burials. Large-scale alterations began with the Capilla Real (late 13th century-early 14th), a pantheon for the kings of Castile. It was altered drastically by the construction of a vast cathedral at its centre in 1523. A UNESCO World Heritage Site.