In January 532 the Nika revolt, a chariot racing riot turned rebellion, burned half of Constantinople along with the second church on the site. The first, the Magna Ecclesia consecrated in 360 by Constantius II, had burned in 404 during riots over the exile of John Chrysostom, and Theodosius II’s replacement of 415, whose lamb frieze was excavated by Alfons Maria Schneider in the 1930s, went up in the revolt. Justinian answered by hiring two geometers, Isidore of Miletus and Anthemius of Tralles, and a workforce of over 10,000. By 537 they had finished a dome 32.6 meters across and only about 0.61 meters thick, carried on pendentives and pierced by 40 windows, set in thick mortar mixed with crushed pottery to flex through earthquakes.

The building then became a trophy for every power that held the city. It survived the earthquake of 869 and the Crusader sack of 1204, and Sultan Mehmed the Conqueror made it a mosque in 1453. Mimar Sinan added buttresses and completed the minarets in the 1500s, and the Fossati brothers wrapped the dome in an iron chain between 1847 and 1849. Atatürk turned it into a museum in 1935, and the World Monuments Fund stabilized its leaking roof from 1997 to 2006. In 2020 Turkey’s Council of State annulled the 1935 decree, and President Erdoğan signed it back into use as a mosque amid criticism from UNESCO and Orthodox church leaders.

• Why whole number ratios like 17 to 12 let laborers build curved vaults with standard bricks and string
• The 40 windows that cut weight at the dome’s base and made it look hung from heaven by a golden chain
• The Venetian doge Enrico Dandolo, who led the 1204 sack, buried on the building’s floor
• The Fossati brothers uncovering, documenting, and then covering the Byzantine mosaics again
• A court ruling that put Mehmed’s 1453 endowment deed above secular law, and the automated curtains that hide the mosaics during prayer