The Hagia Sophia combines a longitudinal basilica and a centralized building in a wholly original manner, with a huge 105-foot (32-metre) main dome supported on pendentives and two semidomes, one on either side of the longitudinal axis. In plan the building is almost square. There are three aisles separated by columns with galleries above and great marble piers rising up to support the dome. The walls above the galleries and the base of the dome are pierced by windows, which in the glare of daylight obscure the supports and give the impression that the canopy floats on air.