The Byzantine style of architecture began in the fifth century. It started in Italy and eventually dominated the eastern part of the Roman Empire. It got its name from the capital city Byzantium (now known as Istanbul). Many significant buildings have been built in the Byzantine form; such as the Hagia Sophia (Turkey) and St. Basils cathedral (Moscow).
The main characteristic of Byzantine churches is having a circular dome over a square base. This is achieved by building arches or triangular supports over the corners of the square floor, basically turning the square into an octagon, and building the dome over them.
Byzantine domes are built out of thin, mortared together bricks. They are relatively plain on the outside but on the inside they are decorated with spiritual paintings. The insides of the churches usually have intricate designs and paintings on their walls.