Hagia Sophia stands in Istanbul, Turkey, on the historic peninsula overlooking the Bosporus. The building has served as a cathedral, mosque, museum, and mosque during different periods of its history.
The present structure was commissioned by the Byzantine emperor Justinian I and completed in 537. For nearly a thousand years it was the cathedral of Constantinople, the capital of the Byzantine Empire. After the Ottoman conquest of Constantinople in 1453, it became an imperial mosque.
Hagia Sophia became a museum in 1935 and was reconverted into a mosque in 2020. Its huge dome, pendentives, mosaics, marble decoration, and long history make it a landmark of both Byzantine and Ottoman architecture. Istanbul was formerly known as Constantinople, but the city's modern official name is Istanbul.