Ancient country, northwestern Anatolia.
Bounded by the Sea of Marmara , the Bosporus , and the Black Sea , it was settled by Thracians in the late 2nd millennium BC. They never submitted to Alexander the Great , and by the 3rd century BC a powerful Hellenistic kingship had been established in the area. There followed a century of inept leadership and rapid decline. Bithynia's last king, Nicomedes IV, bequeathed his kingdom to the Romans in 74 BC.