Hagia Sophia ; (Turkish: Ayasofya, from the Greek: Ἁγία Σοφία "Holy Wisdom") is a former patriarchal basilica, later a mosque, now a museum in Istanbul, Turkey. Famous in particular for its massive dome, it is considered the epitome of Byzantine architecture and to have "changed the history of architecture". It was the largest cathedral in the world for nearly a thousand years, until the completion of the Seville Cathedral in 1520. The current building was originally constructed as a church between 532 and 537 A.D. on the orders of the Byzantine Emperor Justinian, and was in fact the third Church of the Holy Wisdom to occupy the site (the previous two had both been destroyed by riots).
In 1453, Constantinople was conquered by the Ottoman Turks and Sultan Mehmed II ordered the building to be converted into a mosque. The bells, altar, iconostasis, and sacrificial vessels were removed, and many of the mosaics were eventually plastered over. The Islamic features — such as the mihrab, the minbar, and the four minarets outside — were added over the course of its history under the Ottomans. It remained as a mosque until 1935, when it was converted into a museum by the Republic of Turkey.