The Byzantine Empire was the eastern half of the Roman Empire, which survived for a thousand years after the western half had crumbled into various feudal kingdoms and which finally fell to Ottoman Turkish onslaughts in 1453.
The city of Byzantium grew from an ancient Greek colony founded on the European side of the Bosporus.
In AD 330 the Roman emperor Constantine I, in an attempt to strengthen the empire, refounded Byzantium as Constantinople, the 'New Rome' and capital of the eastern half of the empire.
At his death in 395 Emperor Theodosius I divided the empire between his two sons, and it was never reunited.
Theodosius also made Christianity (Eastern Orthodox) the sole religion of the empire, and Constantinople assumed preeminence over other Christian centers in the East as Rome did in the West.
The fall of Rome to the Ostrogoths in 476 marked the end of the western half of the Roman Empire. The eastern half continued as the Byzantine Empire, with Constantinople as its capital. Constantine the Great wanted this city to be built from scratch as the center of the Christian world. The origional Christianity religion Eastern Orthodox church split into differnent factions, The great schism between Eastern and Western churches was mutually agreed to in 1054.