terms, promoting the idea of the new Umayyad caliphs in Cordoba as having a universal prerogative in the Islamic world. Dome of the Villaviciosa Chapel In the nave or aisle of the hypostyle hall which leads to the mihrab, at the spot which marks the beginning of Al-Hakam's 10th-century extension, is a monumental ribbed dome with ornate decoration. The ribs of this dome have a different configuration than those of the domes in front of the mihrab. Their intersection creates a square space in the center with an octagonal scalloped cupola added over this. In total, this intersection of ribs creates 17 vaulted compartments of square or triangular shape, in different sizes, each further decorated with a variety of miniature ribbed domes, star-shaped mini-domes, and scalloped shapes. The space under this dome was surrounded on three sides by elaborate screens of interlacing arches, similar to those of the maqsura but even more intricate. This architectural ensemble apparently marked the transition from the old mosque to Al-Hakam II's expansion, which some scholars see as having a status similar to a "mosque-within-a-mosque". The dome is now part of the Villaviciosa Chapel, while two of the three intersecting arch screens are still present (the western one has disappeared and been replaced by the 15th-century Gothic nave added to the chapel). Like the ornate decorative arches, this dome and the other ribbed domes of the maqsura were highly influential in subsequent Moorish architecture of the period, appearing also in simpler but imaginative forms in the small Bab al-Mardum Mosque in Toledo and giving rise to other ornamental derivations like the much later stucco domes of the Great Mosque of Tlemcen and the Great Mosque of Taza. The courtyard The courtyard is known today as the Patio de los Naranjos or "Courtyard of the Orange Trees". Until the 11th century, the mosque courtyard (also known as a sahn) was unpaved earth with citrus and palm trees irrigated at first by rainwater cisterns and later by aqueduct. Excavation indicates the trees were planted in a pattern, with surface irrigation channels. The stone channels visible today are not original. As in most mosque courtyards, it had fountains or water basins to help Muslims perform ritual ablutions before prayer. The arches that marked the transition from the courtyard to the interior of the prayer hall were originally open and allowed natural light to penetrate the interior, but most