Hagia Sophia Dome

Hagia Sophia in Istanbul (ancient Constantinople) was built for the Byzantine emperor Justinian I between 532 and 537. Its vast central dome, seemingly floating above a ring of windows, was the largest of its time and set the model for Byzantine and later Ottoman domed architecture.

Design

The architects were Anthemius of Tralles and Isidore of Miletus. Their key structural device was the pendentive: curved triangular sections of masonry that make the transition from the square plan of four great piers to the circular base of the dome. Semi-domes to the east and west extend the covered space.

Collapse and rebuilding

The first dome proved too flat. Earthquakes in 553 and 557 cracked it, and in 558 part of the structure, including the eastern semi-dome, collapsed. Isidore the Younger rebuilt the vault about 6.25 m (20.5 ft) higher using lighter materials, as a ribbed dome on pendentives with a diameter of about 32.7-33.5 m (107-110 ft). The reconstruction was completed in 562. The interior height reached about 55.6 m (182 ft).

Later failures

• 989: an earthquake brought down the western dome arch. The Armenian architect Trdat rebuilt the west side with 15 dome ribs; the church reopened on 13 May 994.
• 1346: cracks from an earthquake in October 1344 led to partial collapses on 19 May 1346. Repairs by Astras and Peralta began in 1354.

Roof covering

The dome's outer covering has been repaired many times. In the 20th century cracking of its copper roof contributed to deterioration that prompted international conservation funding, including grants from the World Monuments Fund.

Status

Hagia Sophia is part of the UNESCO World Heritage Site "Historic Areas of Istanbul", inscribed in 1985.

Significance

The building showed how a large dome could be raised over a square plan, a problem central to later church and mosque roofing. Its repeated collapses also made it an early, well-documented case study in the effects of earthquakes on masonry roofs.