A mihrab is a niche inside one of the walls of the mosque, which serves to indicate the direction, or qibla, towards the holy city of Mecca. In fact, during prayer every Muslim is supposed to turn towards the holy place where the Kaaba, the ancient cubic structure at the centre of the Great Mosque, is located. The niche, probably derived from Byzantine architecture, had a semicircular or octagonal base and could be richly decorated with mosaics or polychrome marble.