Byzantine Architecture began in the fifth century in Byzantium (now Istanbul) as a response to the Orthodox church. A major church design was the Vaulted Centralized Church. Another form of Byzantine church was the very uncommon, but present long basilica. Hagia Sophia in Constantinople is a very good example of the centralized church. In a centralized church, a circular dome is supported by triangular supports on a square base. In effect, the triangular supports in the corner of the square made the space below the dome an octagon. This transition from circle to square was a major contribution to architecture.
The insides of the churches were decorated with mosaics because Icons were forbidden. But after a while, they ban was lifted and the Byzantine artists began to paint these icons, Portraits of sacred personages, highly stylized and usually painted in a strictly frontal view on a small panel, over everything. The insides of the Byzantine churches began to look like representations of the Religious world at the time.
In about the twelfth century, Byzantine architecture began to spread. It was introduced to Russia, and the consequence was the beautiful St. Basils Cathedral. The domes on top of the towers were a contribution of Russian architects from the Russian Orthodox Church