Hagia Sophia (Church of Holy Wisdom), is now known as the Ayasofya Museum, is a former Eastern Orthodox church converted to a mosque, now converted into a museum. It was built by emperor Justinian I between 527 and 565 after fire destroyed the original church.

It was converted to a mosque after the Fall of Constantinople to the Ottoman Turks under Sultan Mehmed II in 1453. Since more conservative factions of Islam consider the depiction of the human form to be blasphemous, its mosaics were covered with plaster. The 19th century restoration of the Fossati brothers, who also built a pulpit (minbar) and the four circular medallions hanging on the walls of the nave that bear the names of Muhammad and the first caliphs, is widely deemed to have destroyed much of the original mosaics.

In 1935, under the order of Turkish president Kemal Atatürk, Hagia Sophia was secularized and turned into the Ayasofya Museum.

It is universally acknowledged as one of the greatest buildings of the world and sometimes considered the Eighth Wonder of the World. Its loss to the Ottomans at the fall of Constantinople is considered one of the great tragedies of Christendom by the Greek Orthodox faithful.

There are just 3 larger church after Hagia Sophia all around the world. They are St. Paul's Cathedral in London, St.Peter's Basilica in Vatican and Duomo in Milan.