 In the early 4th century (AD 330), Roman Emperor Constantine the Great had established the city of Constantinople (formerly ancient Byzantium) as the capital of the Roman Empire, later called "Byzantine Empire" by modern historians.The Eastern Roman Empire included lands south-west of the Black Sea and bordering on the Eastern Mediterranean and parts of the Adriatic Sea.This division into Eastern and Western Roman Empires was reflected in the administration of the Roman Catholic and Eastern Greek Orthodox churches, with Rome and Constantinople debating over whether either city was the capital of Western religion.