Byzantine

Byzantine churches are built of brick, often banded with stone, and centered on domes. A dome rests on four arches over a square, and pendentives, curved triangles of masonry, fill the corners between the arches and the dome's round base. Exteriors are mostly plain brick; interiors are lined with marble panels and mosaics of colored glass and gold cubes. From the 9th century the usual plan was the cross-in-square: a central dome over a square, four equal arms, and smaller domes or vaults at the corners.

Hagia Sophia in Istanbul (532-537) has a main dome about 32 m across with a ring of 40 windows at its base. San Vitale in Ravenna, consecrated in 547, is an octagonal church with mosaics of Emperor Justinian and Empress Theodora. The monasteries of Hosios Loukas and Daphni in Greece keep 11th-century mosaics, and St. Mark's Basilica in Venice, rebuilt in the 11th century, follows a Byzantine plan with five domes.

Constantine the Great made Constantinople, today's Istanbul, the capital of the Roman Empire in 330. Under Emperor Justinian I, Anthemius of Tralles and Isidore of Miletus built Hagia Sophia between 532 and 537, using pendentives to carry its dome over a square bay. An earthquake brought down the first dome in 558, and Isidore the Younger rebuilt it about 6 m higher by 562. Hagia Sophia remained the world's largest church for more than 500 years.

From the 9th century, builders put up smaller cross-in-square churches. The style spread with Orthodox Christianity to the Balkans and to Kievan Rus', where St. Sophia's Cathedral in Kyiv was built in the 11th century. The mosaics and frescoes of the Chora Church in Constantinople date from about 1315-1321. The Ottoman conquest of 1453 ended the empire, and Hagia Sophia became a mosque; Ottoman architects adapted its dome and half-domes for mosques such as the Süleymaniye (1550-1557). In the 19th century, Byzantine Revival produced Westminster Cathedral in London and the Alexander Nevsky Cathedral in Sofia.