Hagia Sophia, officially the Hagia Sophia Grand Mosque and formerly the Church of Hagia Sophia, is a Late Antique place of worship in Istanbul. Built in 537 as the patriarchal cathedral of the imperial capital of Constantinople, it was the largest church of the eastern Roman Empire, except during the Latin Empire from 1204 to 1261, when it became the Roman Catholic cathedral. In 1453, after the Fall of Constantinople to the Ottoman Empire, it was converted into a mosque. In 1935 the secular Turkish Republic established it as a museum. In 2020, it was re-opened as a mosque.