Nicomedia (; Greek: , Nikomedeia; modern zmit) was an ancient Greek city located in what is now Turkey. In 286 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 (293324).

The Tetrarchy ended with the Battle of Chrysopolis (skdar) in 324, when Constantine defeated Licinius and became the sole emperor. In 330 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.

Edward Gibbon (; 8 May 1737 – 16 January 1794) was an English historian, writer, and member of parliament. His most important work, The History of the Decline and Fall of the Roman Empire, published in six volumes between 1776 and 1788, is known for the quality and irony of its prose, its use of primary sources, and its polemical criticism of organised religion.