Constantinople
Constantinople (; ) was the capital city of the Roman/Byzantine Empire (330–1204 and 1261–1453), and also of the brief Crusader state known as the Latin Empire (1204–1261), until finally falling to the Ottoman Empire (1453–1923). It was reinaugurated in 324 from ancient Byzantium as the new capital of the Roman Empire by Emperor Constantine the Great, after whom it was named, and dedicated on 11 May 330. The city was located in what is now the European side and the core of modern Istanbul.
İzmit
Nicomedia remained as the eastern (and most senior) capital of the Roman Empire until Licinius was defeated by Constantine the Great in 324. Constantine mainly resided in Nicomedia as his interim capital city for the next six years; until in 330 he declared the nearby Byzantium as "Nova Roma", which eventually became known as Constantinople. Constantine died in a royal villa at the vicinity of Nicomedia in 337. Owing to its position at the convergence of the Asiatic roads leading to the new capital, Nicomedia retained its importance even after the foundation of Constantinople.