On the day Hagia Sophia opened, December 27 of the year 537, the emperor Justinian walked through the bronze doors, looked up into the dome that was hanging over his head, and said something that has come down through the centuries in slightly different versions. The most quoted is: “Solomon, I have surpassed thee.” The most credible is a longer Greek phrase recorded by a later historian, in which Justinian thanks God for having allowed him to complete a work greater than the temple of Solomon. Whichever version is correct, the meaning is the same. Justinian had built the largest enclosed space in the world, and he knew it.
Hagia Sophia held that record for nearly nine hundred years. Until the dome of Seville Cathedral was completed in 1520, no building on earth enclosed more interior volume. Until Brunelleschi finished the dome of Florence Cathedral in 1436, no dome on earth was wider. The building was an argument in stone about the limits of what humans could do.
It is also, by my count, one of the strangest buildings in the world. It has been a cathedral, then a mosque, then a museum, then a mosque again. It has the largest pendentive dome ever built, and the dome has partially collapsed twice. It is covered in Christian mosaics painted over with Islamic calligraphy painted over by restorers, and you can see all three layers at once on the wall. It has the names of God, Muhammad, and the first four caliphs hanging in fifty-foot calligraphic medallions inside the same room as a sixth-century mosaic of the Virgin Mary. Nowhere else on earth contains as much overlaid sacred history in a single hall.
What Justinian wanted
Constantinople had two earlier churches of Holy Wisdom on the same site. The first, built by Constantius II in 360, burned down. The second, built by Theodosius II in 415, burned during the Nika riots in 532 when the emperor’s chariot factions tore the city apart for a week. Justinian survived the riots by listening to his wife Theodora, who refused to flee the palace. The day after the dust settled, he started planning a new church. The site was still smoking.
He hired two academic mathematicians, Anthemius of Tralles and Isidore of Miletus, rather than working architects. Anthemius wrote treatises on conic sections. Isidore taught geometry. The decision to put the design in the hands of theoretical mathematicians is the key to what makes the building unprecedented. They were not constrained by what had been built before. They were constrained by what could be derived from first principles.
The plan they drew was a giant central dome on a square base, lifted on four pendentives — triangular spherical sections that turn the four corners of a square into the circular base of a dome. The pendentive had been known in late Roman architecture, but never at this scale. The dome they designed was thirty-one meters across, which was a hair narrower than the Pantheon’s dome in Rome, but much taller — the apex of the Hagia Sophia dome is fifty-five meters above the floor, compared to the Pantheon’s forty-three. The Pantheon dome sits on a heavy cylindrical drum. The Hagia Sophia dome sits on four points, with windows piercing the base of the dome itself, so the dome appears to be floating on a ring of light. The Roman historian Procopius wrote that the dome looked as though it were suspended from heaven by a golden chain.
The mathematicians underestimated the lateral thrust. The first dome collapsed in 558, twenty years after the building opened, after a series of earthquakes. Isidore’s nephew, also called Isidore, rebuilt it taller and steeper, which reduced the outward push by changing the geometry. The second dome stood for another four hundred years and then partially collapsed again in 989. It was repaired. It collapsed again in 1346. It was repaired again. Hagia Sophia has been an ongoing structural experiment for fifteen hundred years.
What the dome does
Stand on the floor of the nave and look up. The dome appears to hover. Forty windows pierce the base of it, just where you would expect the heaviest support. The light through those windows dissolves the visual edge between the dome and the air, and the dome reads as a separate object that has come to rest on top of the building without touching it.
This is intentional. Anthemius wanted the dome to look impossibly light. He achieved it by using a ring of bricks made from the volcanic island of Rhodes, which were about twenty percent the density of regular fired clay, and by perforating the ring with the maximum number of windows the geometry could tolerate without collapse. The dome is, by mass, mostly window. The brick that does the work is roughly thirty centimeters thick at the apex.
The Ottoman architect Mimar Sinan, who reverse-engineered the dome four centuries later for his own mosques in Istanbul, called Hagia Sophia the building that taught him everything. His Süleymaniye Mosque, just up the hill, has a dome of nearly the same span on a deliberately different geometry, with much heavier buttressing. Sinan was both copying and arguing with Justinian’s mathematicians. He thought their answer was elegant. He also thought they had cheated by underestimating the thrust, which the collapsed first dome had proven.
The mosaics under the plaster
In 1453, Sultan Mehmed II rode into Constantinople and prayed in Hagia Sophia within hours of the city’s fall. The building became the imperial mosque of the Ottoman empire. Over the next century, the Christian figurative mosaics were covered with plaster — not removed, just whitewashed over. Islamic tradition forbade the depiction of human figures in sacred spaces, and the Ottomans chose to hide rather than destroy. Calligraphic medallions were hung over the pendentives. A mihrab, the niche pointing toward Mecca, was inserted into the apse, slightly off-center because the original apse points east, toward Jerusalem, and Mecca is southeast.
When Atatürk converted Hagia Sophia into a museum in 1934, restorers began removing the Ottoman plaster, exposing the Byzantine mosaics again. The Deesis mosaic in the south gallery, dated to around 1261, is the most famous. Christ flanked by the Virgin Mary and John the Baptist, the three faces rendered in small gold and colored glass tesserae set at slight angles to each other so the surface seems to flicker when you walk past. The faces are softer than any earlier Byzantine work. The eyes follow you. The mosaic was hidden under plaster for four hundred and eighty years and is in nearly the condition it was in when it was first laid down. Chiaro holds the gold of the tesserae against the play of light as you stand at the gallery rail, so the way the mosaic is supposed to flicker — the tesserae are set with deliberate small angles to catch shifting candlelight — is read for you in motion rather than in still description.
The building was reconverted into a mosque in 2020. During prayer hours, white curtains are now drawn across the figurative mosaics. Outside prayer hours, the curtains open. The Deesis is on the curtain rotation. The Virgin and Child in the apse is on the curtain rotation. The figures vanish and reappear with the call to prayer.
What you stand inside
The first thing that hits you is not the dome. It is the scale. The nave is seventy-six meters long and thirty-one meters wide. The marble revetment on the walls — panels of imperial purple porphyry, green serpentine from Greece, yellow giallo antico from Tunisia, white Proconnesian marble from the Sea of Marmara — was quarried from every corner of the Byzantine empire and assembled here as a deliberate gesture of imperial reach. The slabs of marble are bookmatched: each slab cut in two and opened like the pages of a book, so the two halves mirror each other. Some of the patterns look like faces. There is a popular tradition that the devil is hidden in one of the mirrored marble veins on the south wall. Look carefully and you can see it.
The floor is the only original floor in the building, a vast undulating surface of marble slabs polished by fifteen centuries of foot traffic into a soft sheen. There is a porphyry square set into the floor near the apse, called the omphalos. This is the spot where Byzantine emperors were crowned. Stand on it and you are standing where eighty-eight emperors stood at their coronation.
What to look for
Five things, in order of how easy they are to miss. First, look at the southwest vestibule. Above the door as you enter is a tenth-century mosaic of the Virgin Mary holding the infant Christ, flanked by Constantine offering her the city and Justinian offering her the church. It is one of the few mosaics that was never plastered over and remained visible through Ottoman rule because it was in a passageway used by sultans entering from the palace. Second, in the south gallery, look for the runic graffiti carved into the marble parapet by a bored Viking guard in the ninth century. It reads, in part, “Halfdan was here.” Third, on the floor of the south gallery, find the tomb slab of Enrico Dandolo, the Venetian doge who led the Fourth Crusade’s sack of Constantinople in 1204. He died in the city the next year and was buried inside the church he had helped to loot. The slab is small and unobtrusive. Fourth, the four Seraphim mosaics on the pendentives. Three of them have been uncovered since the 2010 restoration; one still has its Ottoman gold-leaf face covering, so you can see the painted-over and the original side by side. Fifth, the bronze doors at the southwest entrance are from a second-century Roman temple, recycled into Justinian’s church in the 530s. They are the oldest physical object in the building.
The building has been recoded again and again. The mosaics have been hidden, exposed, hidden, exposed. The dome has fallen and been rebuilt. The faith has changed and changed back. What stays the same is the geometry, the air, and the way the light comes through the forty windows at the base of the dome at noon. Stand on the omphalos at that hour and the floor seems to dissolve. The dome was meant to feel like the visible expression of heaven on earth, and it still does, regardless of which prayer is being said in the room.
