In 532, riots in Constantinople burned the city's cathedral. Justinian rebuilt it at once, on a scale no one had tried. He chose two scholars of mathematics and engineering, Anthemius of Tralles and Isidore of Miletus, as architects. The new church of Hagia Sophia, Greek for "Holy Wisdom," was finished in about five years, from 532 to 537.
The challenge was to put a round dome over a square space. Romans had built domes on round walls, like the Pantheon's. Here, four huge arches stand on four piers around a square, and between the arches curved triangles of masonry, called pendentives, rise and lean inward until they form a ring. The dome, about 31 meters across, sits on that ring. Half-domes at the east and west extend the space into a long oval.
Key idea
Why it works
Looking closely: Hagia Sophia. From outside, a great low dome rises over a mass of half-domes and buttresses that step down around it like a hillside. Inside, the space opens upward: arches, half-domes and the dome itself rise one above another, and light pours in through the windows at the dome's base. Its walls were sheathed in colored marble and its vaults in gold mosaic. In 1453 the Ottoman Turks captured Constantinople, and the church became a mosque, with a mihrab, a minbar and, over time, four minarets. It was a museum from 1934 and is used as a mosque again today, open to visitors.
Worked example: How does a round dome sit on a square?
- Four great arches span the four sides of the square, resting on four piers at the corners.
- Between each pair of arches, a curved triangle of masonry (a pendentive) fills the corner and leans inward.
- The four pendentives meet in a circle at the top, and the dome sits on that circle.
Answer: Arches on piers, pendentives in the corners, and the dome on the ring they make.
Common mistake