Short answers, pulled from the story.
Byzantine architecture is dated from AD 330, when Constantine the Great established the new Roman capital at Byzantium (later Constantinople), to the fall of the Byzantine Empire in 1453. The style had no hard boundary with late Roman architecture at its outset.
The Hagia Sophia in Constantinople is the most famous example of Byzantine architecture. Originally completed in 360 and rebuilt in its final form under Emperor Justinian in 537, it held the title of largest church in the world until the Ottomans took Constantinople in 1453.
Byzantine architects invented pendentives, a system that provides a smooth structural transition from a square floor plan to a circular dome. This breakthrough occurred during the reign of Emperor Justinian and is exemplified in the Hagia Sophia, where the central dome spans a square of roughly 100 feet.
During the Umayyad Caliphate era from 661 to 750, Byzantine arts formed a fundamental source for early Islamic building, particularly in Syria. The tile work, geometric patterns, multiple arches, domes, and polychrome brick and stone characteristic of Muslim and Moorish architecture were heavily influenced by Byzantine precedents. Monuments built in Syria between 709 and 715 show clear Byzantine references in both plan and decoration.
Patricios identified seven types: the basilican plan, the domed basilica, the cruciform plan, the centralised plan, the converted temple, the cross-in-square (dominant from the ninth century), and the Athonite plan created in the tenth century. The cross-in-square became the most widely used form over time.
Byzantine columns mostly developed from the classical Corinthian order but departed from it by using drills to undercut ornamentation and nearly abandoning fluted shafts. Stone blocks were left rough from the quarry and carved to each sculptor's own design, meaning repetitions of the same capital are rare. One celebrated design features leaves carved to look as if blown by wind, found in the 7th-century Hagia Sophia in Thessaloniki.