The architecture of the Christian Roman empire in the East, centred on Constantinople: domes carried on pendentives over square bays, brick and mortar construction, and interiors sheathed in marble and gold mosaic, from Justinian’s Hagia Sophia to the small, many-domed cross-in-square churches of the middle and late empire.
When Constantine refounded Byzantium as Constantinople in 330, the new capital built basilicas like those of Rome. But the eastern empire inherited, from Roman and Hellenistic practice, a strong tradition of vaulting in brick, and in the sixth century its architects put the dome at the centre of the church. The decisive device was the pendentive: the spherical triangle that fills each corner between four arches, so that a circular dome can rest on a square. Earlier builders in Persia and the Caucasus used the squinch, an arch or niche across the corner that turns the square into an octagon; both methods run through Byzantine building.
The age of Justinian (527–565) produced the masterpieces. Sts Sergius and Bacchus in Constantinople (c. 527–536) and San Vitale in Ravenna (consecrated 547) are domed octagons wrapped in ambulatories and galleries. Hagia Sophia (532–537), designed by Anthemius of Tralles and Isidore of Miletus, joined the basilica and the dome: a central dome some 31 m across on four pendentives, extended east and west by semidomes that open in turn into smaller exedrae, so that the space seems to unfold beneath a canopy. After an earthquake the dome fell in 558; Isidore the Younger rebuilt it about 6 m higher by 562. Forty windows round its base make it seem to float on light.
Byzantine walls were built of thin bricks in very thick beds of mortar, often in bands with courses of stone; vaults and domes were raised with little or no centring by laying the bricks in rings or inclined courses. Outside, the buildings are modest and their masses show the vaults within; inside, every surface was covered (marble revetment below, gold-ground mosaic above) to make the church an image of heaven.
After the crisis of Iconoclasm (726–843) the typical church became small and centralised. The cross-in-square plan divides a square into nine bays: the central one domed on a drum over four columns or piers, the four arms barrel-vaulted, the corners lower and sometimes domed as well. The Theotokos church at Hosios Loukas, Nea Moni on Chios and the Chora church in Constantinople, with its fourteenth-century mosaics, show the refinement of the type; a screen of icons, the templon that became the iconostasis, divided sanctuary from nave. Exteriors grew decorative, with patterned brickwork and banded cloisonné masonry.
Byzantine architecture spread with Orthodox Christianity to the Balkans, Armenia and Georgia, to Venice (whose St Mark’s copies Justinian’s Holy Apostles) and to Rus’. After the conquest of 1453 Hagia Sophia became a mosque, and its dome became the starting point for the imperial mosques of the Ottoman architects.