Hagia Sophia became an Ottoman mosque after Constantinople was conquered in 1453. Sultan Mehmed II converted the Byzantine cathedral for Islamic worship shortly after taking the city, which he renamed Istanbul in common usage over time.
The building was originally completed in 537 under Byzantine emperor Justinian I. Its enormous dome, pendentives, marble revetments, and monumental interior made it one of late antiquity’s most influential architectural achievements. Ottoman architects preserved much of the structure while adding minarets, a mihrab, a minbar, and other mosque furnishings.
Hagia Sophia served as a mosque for nearly five centuries. In 1935, it opened as a museum under the Turkish Republic, and in 2020 it was reconverted into a mosque. It remains an active place of worship and a major historic landmark.
Hagia Sophia is sometimes confused with Istanbul’s Blue Mosque, but they are separate buildings facing one another across Sultanahmet Square. The Blue Mosque was built centuries later, between 1609 and 1616.