Nicomedia

Nicomedia was an ancient city in the region of Bithynia in northwestern Asia Minor, situated on the Gulf of Izmit near the present-day city of Izmit in Turkey. The city was named for King Nicomedes I of Bithynia, who is traditionally credited with refounding it as the royal capital in the Hellenistic period. As the seat of power in the Bithynian kingdom, Nicomedia grew into a major urban center and a symbol of political authority in the region.

Under Roman rule, Nicomedia remained an important provincial capital and commercial hub. In the late 3rd and early 4th centuries CE, during the Tetrarchy established by Diocletian, the city served as an imperial residence and one of the eastern capitals of the empire, hosting a substantial palace complex and extensive fortifications. Its strategic location near major routes and the frontier contributed to its prominence in administration, defense, and trade. Nicomedia also developed as a religious center, with a significant bishopric within the province of Bithynia et Pontus.

In late antiquity and the early Byzantine period, the city continued to be influential, but its relative importance declined as Constantinople rose in political and ceremonial prominence after 330 CE. The site later came under Byzantine and, ultimately, Ottoman control. Today, the ancient site corresponds to the modern Turkish city of Izmit, and archaeological remains—including walls, public buildings, and other urban remnants—reflect its historical status as a major urban center in northwestern Anatolia.