diverse extraction irregularly distributed, of a form that in occasions predominate those of paleo-Christian, Visigothic or Asturian origin, while at other times emphasizes the Muslim impression. The churches have usually basilica or centralized plans, sometimes with opposing apses. Principal chapels are of rectangular plan on the exterior and ultra-semicircular in the interior. The horseshoe arch of Muslim evocation is used, somewhat more closed and sloped than the Visigothic as well as the alfiz. Geminated and tripled windows of Asturian tradition and grouped columns forming composite pillars, with Corinthian capital decorated with stylized elements. Decoration has resemblance to the Visigothic based in volutes, swastikas, and vegetable and animal themes forming projected borders and sobriety of exterior decoration. Some innovations are introduced, as great lobed corbels that support very pronounced eaves. A great command of the technique in construction can be observed, employing ashlar, walls reinforced by exterior buttresses and covering by means of segmented vaults, including by the traditional barrel vaults. The architecture of Al-Andalus Emirate and Caliphate of Córdoba The Muslim conquest of the former Visigothic Kingdom by the troops of Musa ibn Nusair and Tariq ibn Ziyad, and the overthrowing of the Umayyad dynasty in Damascus, eventually led to the creation of an independent emirate by Abd ar-Rahman I, the only surviving Umayyad prince who escaped from Abbasids, and established his capital city in Córdoba. It served as the capital of Al-Andalus from 750 to 1010, with its political and cultural apogee taking place during the new Caliphate period in the 10th century. In Cordoba, Abd ar-Rahman I built the Great Mosque in 785. It was expanded multiple times up until the 10th century, and after the Reconquista it was converted into a Catholic cathedral. Its key features include a hypostyle hall with marble columns supporting two-tiered arches, a horseshoe-arch mihrab, ribbed domes, a courtyard (sahn) with gardens, and a minaret (later converted into a bell tower). Abd ar-Rahman III, at the height of his power, began construction of Madinat al-Zahra, a luxurious palace-city to serve as a new capital. It played a major role in formulating a more distinct "caliphal" style which was crucial in the development of subsequent Andalusi architecture. On a smaller scale, the Bab al-Mardum Mosque (later converted to a church) in Toledo is a well-preserved example of a small neighbourhood mosque built at the end of the Caliphate period. The Taifas The Caliphate disappeared