Nicomedia

Nicomedia (; Greek: Νικομήδεια, Nikomedeia; modern İzmit) was an ancient Greek city located in what is now Turkey. In 286 AD, Nicomedia became the eastern and most senior capital city of the Roman Empire (chosen by the emperor Diocletian who ruled in the east), a status which the city maintained during the Tetrarchy system (293–324 AD).

The Tetrarchy ended with the Battle of Chrysopolis (Üsküdar) in 324 AD, when the western Roman emperor Constantine the Great defeated Licinius and became the sole emperor. In 330 AD, Constantine chose for himself the nearby Byzantium (which was renamed Constantinople, modern Istanbul) as the new capital of the Roman Empire.

The city was incorporated into the Ottoman Empire with the victory of Sultan Orhan Gazi against the Byzantine Empire. The Byzantines managed to retake it in the aftermath of the Battle of Ankara, but it fell definitively to the Ottomans in 1419 AD.