After the Nika Riots burned much of Constantinople to the ground in 532, Justinian decided to raise on the ruins the largest covered space the ancient world had ever seen. The architects were the mathematician Anthemius of Tralles and the geometer Isidore of Miletus — the building was conceived not by an architect but by two scientists.

The project took only five years and eleven months. The resulting dome was roughly 32 metres across, pierced by forty windows around its drum, and seemed to hang in the air almost without support. Procopius wrote that it appeared "to be suspended from heaven by a golden chain." Structurally it was a gamble: the first dome collapsed in an earthquake in 558 and was rebuilt in 562, higher and lighter.

Inside, marbles came from every corner of the empire — green Thessalian, red Egyptian porphyry, white Marmara. Gold mosaics covered the surfaces, and where they met the light pouring through forty windows the walls appeared to lose their substance. This is the central move of Byzantine aesthetics: solid architecture dissolves in light and colour; space becomes the earthly representation of heaven.

Hagia Sophia remained the largest church in Christendom for a thousand years. After the Ottoman conquest of Constantinople in 1453 it was converted to a mosque; Sinan reinforced it structurally under Selim II and Murad III and added four minarets. By decree of Atatürk it became a museum in 1934, and was reconverted to a mosque in 2020. The building still stands — fifteen hundred years on top of a major fault line, one of the longest-functioning great religious buildings in the world.