The Byzantine period starts with the division of the Roman empire to East and West. The collapse of the Western Roman Empire that followed this division accentuated the position of the Greeks in the empire and eventually allowed them to become identified with Eastern part of the empire (Byzantine) altogether. Constantinople became the center of the empire, and the center of Hellenism, when Constantine the Great turned Byzantium into the new capital of the Roman Empire, from then on to be known as Constantinople.
The Byzantine Empire was the predominantly Greek-speaking eastern half continuation and remainder of the Roman Empire during Late Antiquity and the Middle Ages. Its capital city was Constantinople, originally founded as Byzantium (hence the term Byzantine). The Byzantines survived the fall of the Western Roman Empire in the 5th century AD and continued to exist for another thousand years until Constantinople fell to the Ottoman Turks in 1453. During most of its existence, the Byzantine empire was the most powerful economic, cultural, and military force in Europe.