When did Hagia Sophia become a museum?
Hagia Sophia
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From the date of its construction in 537 until 1453, it served as an Eastern Orthodox cathedral and the seat of the Ecumenical Patriarch of Constantinople,[4] except between 1204 and 1261, when it was converted by the Fourth Crusaders to a Roman Catholic cathedral under the Latin Empire. The building was later converted into an Ottoman mosque from 29 May 1453 until 1931. It was then secularized and opened as a museum on 1 February 1935.[5] It remained the world's largest cathedral for nearly a thousand years, until Seville Cathedral was completed in 1520.