It was designed by the Greek geometers Isidore of Miletus and Anthemius of Tralles.
It remained a mosque until 1931, when it was closed to the public for four years.
It was re-opened in 1935 as a museum by the Republic of Turkey.
Hagia Sophia was, as of 2014, the second-most visited museum in Turkey, attracting almost 3.3 million visitors annually.
By that point, the church had fallen into a state of disrepair.
Nevertheless, the Christian cathedral made a strong impression on the new Ottoman rulers and they decided to convert it into a mosque.
The bells, altar, iconostasis, and sacrificial vessels and other relics were removed and the mosaics depicting Jesus, his Mother Mary, Christian saints and angels were also removed or plastered over.
Islamic features—such as the mihrab, minbar, and four minarets—were added.
) was a Greek Orthodox Christian patriarchal basilica (church), later converted into an Ottoman mosque, and now a museum (Ayasofya Müzesi) in Istanbul, Turkey.
From the date of its construction in 537 AD, and until 1453, it served as an Orthodox cathedral and seat of the Patriarch of Constantinople, except between 12, when it was converted by the Fourth Crusaders to a Roman Catholic cathedral under the Latin Empire of Constantinople. It was then secularized and opened as a museum on 1 February 1935.
It remained the world's largest cathedral for nearly a thousand years, until Seville Cathedral was completed in 1520.
The current building was originally constructed as a church between 532 and 537 on the orders of the Byzantine Emperor Justinian I and was the third Church of the Holy Wisdom to occupy the site, the previous two having both been destroyed by rioters.