The first mosques were simple buildings made of wood and clay. Then, as the world of Islam grew in size and power, large mosques of cut stone and brick were built. Because no Islamic building tradition yet existed, these early mosques were modeled after Christian churches. The oldest existing mosque, the Dome of the Rock in Jerusalem, was built in 691. It has many features of Byzantine Christian churches, including Grecian-style columns and mosaic decorations.
Muslim architects soon began to develop a new type of religious building, designed specifically for Islamic worship. An early example of the new design is the Great Mosque in Damascus, begun about 705. It is entered through a rectangular court with covered passageways on three sides. In the court is a fountain for washing before prayer. The fourth wall of the court is closest to Mecca, the holy city of Islam. All Muslims face in the direction of Mecca when they pray. The wall is marked by a small, arched prayer niche. Over the aisle leading to this niche is a dome. A tower, or minaret, is used to call the faithful to prayer.
Other architects developed variations on this basic style. Some mosques have domes over each end of the aisle leading to the prayer niche. Other mosques have a large central dome. Some domes are ridged on the outside and resemble large melons. Inside, the ceilings of domes are often covered with decorative forms that resemble honeycombs, scales, or stalactites (icicle-like formations found in caves). Many mosques, especially those in Spain, North Africa, and Persia, are covered with tiles. In the 1500's and 1600's mosques became more complex, with many domes and minarets. The Sultan Ahmed Mosque (also called the Blue Mosque), in Istanbul, Turkey, is a typical example.