Is the architecture of the Hagia Sophia Greek or Roman?

The architecture of the Byzantine Empire was a mixture of the earlier Greek and Roman style with Asian / Oriental influences. It often utilized a large dome set on a square base instead of a vaulted roof. Rounded arches and spires also were common features on Byzantine buildings. Bricks of different colors were frequently used on the outside of the structure and arranged so that they appeared as bands or in complex patterns. Inside, the walls were usually made of marble with colored glass mosaics.