Built in 706 AD, the Great Mosque in Damascus is one of the earliest mosques to survive in almost unaltered condition. It was built in the location and on the foundations of a Roman sacred place, under the administration of the great Muslim leader Caliph Al-Walid. The central feature of the mosque is a large courtyard with arcades on three sides. On the fourth side, which faces Mecca, stands the covered part of the mosque known as the sanctuary. It has three aisles running parallel to the quibla wall and a nave, at right-angles to the quibla wall, which led to the caliph's palace. The columns which support the roof come from Roman buildings and two of the three minarets are based on Roman corner towers. There are entrances on each of the four sides. A treasury building stands on Cointhian columns at the east end of the courtyard. This mosque, an architectural interpretation of Muhammad's house in Medina, formalised the place of courtyards in mosque design.