Cross section of Hagia Sophia in Istanbul (historically Constantinople). The Greek name Hagia Sophia means "Holy Wisdom." It is known as Ayasofya in Turkish.
The building was originally constructed as a church between A.D. 532 and 537 on the orders of the Byzantine Emperor Justinian I. In 1453, Constantinople was conquered by the Ottoman Empire under Mehmed the Conqueror, who ordered the building be converted into a mosque. It was closed in 1931 and reopened as a museum in 1935. This important milestone in the history of architecture was the world's largest cathedral for nearly a thousand years. It also greatly influenced the design of Ottoman mosques, including the nearby Blue Mosque.