Constantine the Great (c. 272–337 CE) was famed for winning the battle at the Milvian Bridge, reuniting the Roman Empire under one emperor (Constantine himself), winning major battles in Europe, legalizing Christianity, and establishing a new eastern capital of Rome at the city, Nova Roma, formerly Byzantium, that was to be named Constantinople.
Constantinople (now known as Istanbul) became the capital of the Byzantine Empire, which lasted until it fell to the Ottoman Turks in 1453.