ancient district in northwestern Anatolia, adjoining the Sea of Marmara, the Bosporus, and the Black Sea, thus occupying an important and precarious position between East and West. Late in the 2nd millennium BC, Bithynia was occupied by warlike tribes of Thracian origin who harried Greek settlers and Persian envoys alike. Their remarkable pugnacity kept them from complete Persian domination after the 6th century; in addition, they never submitted to Alexander the Great or his Seleucid successors. By the 3rd century BC the small but powerful state had evolved from tribal government to Hellenistic kingship and reached the height of its power early in the 2nd century BC. There followed a century of inept leadership and rapid decline. Bithynia's last king, Nicomedes IV, little more than a Roman puppet, bequeathed his kingdom to the Romans in 74 BC.