Hagia Sophia (Church of Holy Wisdom), now known as the Ayasofya Museum, is a former Eastern Orthodox church converted to a mosque in 1453, converted into a museum in 1935, in the Turkish city of Istanbul. It is universally acknowledged as one of the greatest buildings of the world and sometimes considered the Eighth Wonder of the World. Its conquest by the Ottomans at the fall of Constantinople is considered one of the great tragedies of Christendom by the Greek Orthodox faithful.

Nothing remains of the first church that was built on the same site during the 4th century. Following the destruction of the first church, a second was built by Constantius, the son of Constantine the Great, but was burned down during the Nika riots of 532. The building was rebuilt under the personal supervision of emperor Justinian I and rededicated on December 27, 537.

Justinian chose Isidore of Miletus and Anthemius of Tralles, a physicist and a mathematician, as architects; Anthemius, however, died within the first year. The construction is described in Procopius' On Buildings (De Aedificiis). The Byzantine poet Paulus the Silentiary composed an extant poetic ekphrasis, probably for the rededication of 563, which followed the collapse of the main dome.

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