Hagia Sophia, Turkish Ayasofya, Latin Sancta Sophia, also called Church of the Holy Wisdom or Church of the Divine Wisdom, cathedral built at Constantinople (now Istanbul, Turkey) in the 6th century ce (532–537) under the direction of the Byzantine emperor Justinian I. By general consensus, it is the most important Byzantine structure and one of the world’s great monuments.
The Hagia Sophia was built in the remarkably short time of about six years, being completed in 537 ce. Unusual for the period in which it was built, the names of the building’s architects—Anthemius of Tralles and Isidorus of Miletus—are well known, as is their familiarity with mechanics and mathematics. The Hagia Sophia combines a longitudinal basilica and a centralized building in a wholly original manner, with a huge 32-metre (105-foot) main dome supported on pendentives and two semi-domes, 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.
The original church on the site of the Hagia Sophia is said to have been ordered to be built by Constantine I in 325 on the foundations of a pagan temple. His son, Constantius II, consecrated it in 360. It was damaged in 404 by a fire that erupted during a riot following the second banishment of St. John Chrysostom, then patriarch of Constantinople. It was rebuilt and enlarged by the Roman emperor Constans I. The restored building was rededicated in 415 by Theodosius II. The church was burned again in the Nika insurrection of January 532, a circumstance that gave Justinian I an opportunity to envision a splendid replacement.
The structure now standing is essentially the 6th-century edifice, although an earthquake caused a partial collapse of the dome in 558 (restored 562) and there were two further partial collapses, after which it was rebuilt to a smaller scale and the whole church reinforced from the outside. It was restored again in the mid-14th century. For more than a millennium it was the Cathedral of the Ecumenical Patriarchate of Constantinople. It was looted in 1204 by the Venetians and the Crusaders on the Fourth Crusade.
After the Turkish conquest of Constantinople in 1453, Mehmed II had it repurposed as a mosque, with the addition of a wooden minaret (on the exterior, a tower used for the summons to prayer), a great chandelier, a mihrab (niche indicating the direction of Mecca), and a minbar (pulpit). Either he or his son Bayezid II erected the red minaret that stands on the southeast corner of the structure. The original wooden minaret did not survive. Bayezid II erected the narrow white minaret on the northeast side of the mosque. The two identical minarets on the western side were likely commissioned by Selim II or Murad III and built by renowned Ottoman architect Sinan in the 1500s.
In 1934 Turkish Pres. Kemal Atatürk secularized the building, and in 1935 it was made into a museum. Art historians consider the building’s beautiful mosaics to be the main source of knowledge about the state of mosaic art in the time shortly after the end of the Iconoclastic Controversy in the 8th and 9th centuries. The Hagia Sophia is a component of a UNESCO World Heritage site called the Historic Areas of Istanbul (designated 1985), which includes that city’s other major historic buildings and locations.