Haghia Sophia, Constantinople

Constantinople was the capital city of the Roman Empire (330–395), the Byzantine Empire (395–1204 and 1261–1453), the brief Crusader state known as the Latin Empire (1204–1261), and the Ottoman Empire (1453–1923).
Hagia Sophia. Built in 537 as the patriarchal cathedral of the imperial capital of Constantinople, it was the largest Christian church of the eastern Roman Empire (the Byzantine Empire) and the Eastern Orthodox Church, except during the Latin Empire from 1204 to 1261, when it became the city's Roman Catholic cathedral. In 1453, after the Fall of Constantinople to the Ottoman Empire, it was converted into a mosque. In 1935 the secular Turkish Republic established it as a museum. In 2020, it re-opened as a mosque.