Key facts

• The dome and the structural revolution: the most structurally consequential single building in the history of world architecture — the dome (the most continuously record-breaking single dome in history: 31.87 m diameter; 55.6 m above the floor; the largest dome in the world from 537 CE until 1436 CE (when Brunelleschi completed the dome of Florence Cathedral at 45.5 m inner span — the most precisely quantified architectural world-record transfer in the history of construction); 899 years as the world’s largest dome — the most continuously held structural record in the history of pre-modern architecture; the perception (the 6th-century historian Procopius of Caesarea wrote that the dome appeared to be “suspended from heaven by a golden chain” — the most precisely described optical illusion in any ancient description of a building; the effect (the circle of 40 windows at the base of the dome creates a band of light that detaches the dome visually from its supporting walls — the most precisely designed single daylighting effect in any ancient interior)); the pendentives (described in overview section; the first large-scale use of this structural solution (a pendentive allows a circular dome to be placed on a square base by transitioning the geometry via curved triangular sections) — the most consequentially adopted single architectural detail in the history of world architecture: the Sultanahmet / Blue Mosque (1616) and the Süleymaniye (1558) in Istanbul; the Selimiye Mosque in Edirne (1575 — the most perfectionist deployment of the pendentive in Ottoman architecture: Sinan’s masterwork); the Pantheon in Rome’s influence on the pendentive; the Capitol dome in Washington (1866) are all the children of this one building))
• The mosaics and the art: the most extensively documented single Byzantine mosaic programme — the mosaics (the most valuable single collection of Byzantine pictorial art in the world: the Hagia Sophia mosaics span 4 centuries (9th–14th CE) — the most extensive single site of Byzantine mosaic production in Turkey; the Deësis mosaic (the most humanistic single face in Byzantine art: the mosaic in the upper gallery showing Christ flanked by the Virgin Mary and John the Baptist; the Christ face is the most naturalistically rendered single human face in any Byzantine mosaic — the most individually expressive single image in the entire Byzantine iconographic tradition; the most precisely dated early example of the shift toward naturalism in Byzantine art (c. 1261) that anticipates the Italian Renaissance)); the seraphim (the most precisely identified single theological image in the building: the four giant seraphim faces at the base of the dome — the largest pre-modern figurative mosaics in the world; the two faces that had been covered by Ottoman medallions were revealed in restoration (2009–2010) — the most consequentially unveiled single Byzantine artwork in modern Turkish heritage conservation))
• The four religious phases and the 2020 conversion: the most politically consequential single building in the history of world heritage — the Cathedral (532–537 construction; the most expensive single building project of the reign of Justinian I — the most ambitious Emperor in the history of the Eastern Roman Empire; the building was consecrated on 27 December 537 CE); the Mosque (1453: Sultan Mehmed II entered Constantinople on 29 May 1453 — the most precisely dated single fall of a Christian imperial capital in history; the same afternoon he walked to Hagia Sophia and ordered it converted to a mosque — the most rapidly executed single religious conversion of a major building in the history of the Ottoman Empire; the minarets were added (1453–1574); the Islamic medallions with the names of Allah, Muhammad, and the first four Caliphs were hung in the nave (1847) — the most artistically incongruous single addition to a Byzantine interior); the Museum (1934: Atatürk signed the decree making Hagia Sophia a secular museum (the most politically significant single use of a heritage building in the history of Turkish nationalism: the conversion to museum status was a founding act of Turkish secular modernism — the most symbolically definitive single gesture of the Kemalist revolution)); the 2020 reconversion (the most internationally debated single heritage decision of the 21st century: a Turkish presidential decree of July 2020 reconverted Hagia Sophia to a mosque — the most condemned single national heritage decision by UNESCO and international religious bodies in the 21st century))
• Heritage: UNESCO World Heritage Site, Historic Areas of Istanbul, inscribed 1985
• GPS: 41.0086° N, 28.9802° E