Hagia Sophia

Hagia Sophia is the former Greek Orthodox Christian patriarchal cathedral, later an Ottoman imperial mosque and now a museum (Ayasofya Müzesi) in Istanbul, Turkey.

Built in AD 360 at the beginning of the Middle Ages, it was famous in particular for its massive dome. It was the world's largest building and an engineering marvel of its time. It is considered the epitome of Byzantine architecture and is said to have "changed the history of architecture".