Constantine I founded Constantinople as the Roman Empire’s eastern capital.
Constantine dedicated the rebuilt city on the site of Byzantium in 330 CE. He called it Constantinople, meaning “City of Constantine,” although the settlement continued to have other names in different periods. Its strategic position beside the Bosporus connected Europe and Asia and placed the city near the empire’s wealthy eastern provinces.
The city was designed with imperial monuments, a palace, churches, forums, aqueducts, and defensive walls. Constantine’s foundation did not instantly erase Rome’s importance, and the empire continued to have multiple administrative centers. Constantinople nevertheless became the principal political center of the eastern Roman world.
The city remained the capital of the Eastern Roman, or Byzantine, Empire for more than a millennium. It fell to the Ottoman Empire in 1453 and later became widely known as Istanbul. This question concerns Constantine’s foundation of the city, not its later Ottoman history.