The present Hagia Sophia in Istanbul was completed in 537 under Emperor Justinian I.
Construction began after the Nika riots destroyed the earlier church in 532. The architects Anthemius of Tralles and Isidore of Miletus designed a vast domed basilica, and the building was dedicated on 27 December 537. Its dome was later rebuilt after earthquake damage in 558.
Hagia Sophia was the cathedral of Constantinople for centuries and became an imperial mosque after the Ottoman conquest in 1453. It was opened as a museum in 1935 and reconverted into a mosque in 2020. The date 537 refers to the dedication of the surviving Justinianic building, not the earlier churches on the site.