As for the Byzantine Empire, they quickly grew in wealth and predominance. Some say they were only a continuation of the Roman Empire since they were the Eastern half of the earlier Empire that continued after the schism; however, the differences are notable. Byzantine art took to glorifying Christianity and serving the needs of the church (not a very Roman ideal). During this time, in fact, the church probably had the most power of anyone. As Christianity became more popular under Constantine, it became necessary to build more churches. Byzantine architecture preferred a central plan to the Roman basilica model, and it utilized piers (massive vertical pillars).
Byzantine builders also made their churches to be "Houses of Mystery" with dramatic lighting, mosaics, and an overall dreamlike setting.
The walls of Hagia Sophia are thin with more windows to make for a more luminous interior. The streaming light from all the numerous windows acted as symbolism for the church-goers, who recognized that Jesus is the light of the world. From here on, light is almost always a symbol of God's presence, and it comes from the lighting in Early Medieval churches.