Hagia Sophia

The Hagia Sophia is a former Orthodox basilica, later a mosque, and now a museum in Istanbul, Turkey.
Cathedral: 360-1453
Roman Catholic Cathedral: 1204-1261
Mosque: 1453-1934
Famous for its massive dome, it is considered the epitome of Byzantine architecture and is said to have changed the history of architecture. It was the largest in the world until Seville Cathedral was complete in 1520. It is the church in which the Great Schism of Christianity started in 1054.
The Hagia Sophia later served as a model for other Ottoman mosques, such as the famous Blue Mosque of Istanbul.