Constantinople was the capital of the Byzantine empire in modern day Turkey.  For centuries the city was not very large, and was called Byzantium. Roman Emperor Constantine the Great renamed it for himself and made it his capital of Roman. As the Western Roman Empire fell, the Eastern Empire continued as the Byzantine empire. n 1453 the Ottoman Turks conquered the Byzantine empire and made it their capital, calling it Istanbul.

Byzantine emperor Justinian built the Hagia Sofia church in Constantinople.