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.