the 11th century. The Great Fatimid Palaces, where the caliphs lived, have not been preserved. After the Fatimids, Egypt became the capital of the Ayyubid dynasty founded by Salah ad-Din (Saladin). The most significant monument of this era was the Citadel of Cairo, which became Egypt's center of government up until the 19th century. In the mid-13th century the Mamluks took control and ruled an empire from Cairo that lasted until the Ottoman conquest of 1517. The Mamluks were major patrons of architecture and a large part of the historic heritage of Islamic Cairo dates from their time. The major monuments of Mamluk architecture were multi-functional religious and funerary complexes whose layouts were adapted to fit into the dense urban environment. Some of the most significant examples of this period include the Complex of Sultan Qalawun, the Madrasa-Mosque of Sultan Hasan, and the Funerary complex of Sultan Qaytbay. Sudan Nubia The Christianization of Nubia began in the 6th century. Its most representative architecture consists of churches, whose design is based on Byzantine basilicas, but which are relatively small and made of mud bricks. Vernacular architecture of the Christian period is scarce. Soba is the only city that has been excavated. Its structures are made of sun-dried bricks, the same as today, except for an arch. During the Fatimid phase of Islam, Nubia became Arabized. Its most import mosque was the Mosque of Derr. West Africa At Kumbi Saleh, locals lived in dome-shaped dwellings in the king's section of the city, surrounded by a great enclosure. Traders lived in stone houses in a section which possessed 12 beautiful mosques (as described by al-Bakri), one of which was for Friday prayer. The king is said to have owned several mansions, one of which was sixty-six feet long and forty-two feet wide, contained seven rooms, was two stories high, and had a staircase, with paintings on the walls and chambers filled with sculpture. Sahelian architecture initially grew from the two cities of Djenné and Timbuktu. The Sankore Mosque, constructed from mud on timber, was similar in style to the Great Mosque of Djenné. Ghana Ashanti Ashanti architecture from Ghana is perhaps best known from the reconstruction at Kumasi, Ghana. Its key features are courtyard-based buildings, and walls with striking reliefs in brightly painted mud plaster. An example is the Besease shrine, which can be seen at Kumasi. Four rectangular rooms, constructed from wattle