What name was historically used for the Turkish city currently known as Istanbul?

The historically used name for the Turkish city currently known as Istanbul is Constantinople. The name derives from the ancient Greek city of Byzantium, which was initially converted into a Roman capital and later renamed Constantinople by Emperor Constantine the Great in AD 330. This name persisted throughout the Byzantine Empire until the Ottoman Empire's conquest of the city in 1453, after which it was renamed Istanbul. The name Constantinople is reflective of the city's rich historical and cultural significance as a former capital of the Roman and Byzantine Empires.