(Βιθυνία), a province in the N.W. of Asia Minor, stretching along the Propontis, the Thracian Bosporus, and the Euxine; between the rivers Rhynadacus in the west, and the Parthenius in the east. In the south it bordered on Galatia and Phrygia Epictetus. The country derived its name from its inhabitants, the Bithyni, whose original home was the country about the Strymon in Thrace. Remnants of this nation remained in Thrace, and are frequently spoken of under the name of Thyni, or Thracian Bithyni. On their arrival in Asia, they expelled or subdued the native tribes of the Myrians, Bebryces, Cancones, and Mygdones; the Mariandyni, however, maintained themselves on the coast in the north-eastern part of the country. The Bithyni, after their conquest of the new country, appear to have been divided into two branches, the Thyni on the coast about the river Sangarius, and the Bithyni in the southern parts of the country. In the reign of Croesus, Bithynia was incorporated with the Lydian empire, together with which it soon after fell into the hands of the Persians. Under the dominion of the latter, who probably made no great changes in the constitution of the country, it was governed by the Satrap of Phrygia; for at that time it scarcely contained any towns except the Greek colonies of Chalcedon and Astacus. During the subsequent disturbances in the Persian empire, some native princes of the Thyni made themselves independent, and maintained this independence even against Alexander the Great and his successors. Nicomedes, the first who assumed the title of king, reigned until n.c. 246. His successor, Prussias I., who died in n.c. 192, and Prussias II., who (probably died in n.c. 150) did much to establish the kingdom on a firm basis, and to extend its boundaries. The last king, Nicomedes III., in n.c. 75, bequeathed his kingdom to the Romans, who at first united it with their province of Asia, and afterwards with Pontus, until Augustus constituted it as a separate proconsular province. At the same time that emperor united the western part of Paphlagonia, under the name of Pontus, with Bithynia. Theodosius II., again divided the province, restricting the name of Bithynia to the western half, which contained the cities of Nicomedia, Nicaea, and Chalcedon, while the eastern part, with the cities of Heraclea and Claudiopolis, received the name of Honorias.

The country of Bithynia is traversed in all directions by woody mountains, the highest of which is the Myrian Olympus, which furnished abundance of timber for shipbuilding. The plains and valleys are very beautiful and fertile, producing barley, wheat, beans of various kinds, figs, and wine, but no olives. The district about Bithynium was distinguished for its excellent pasture; and the cheese made there was in great repute among the ancients. The principal river was the Sangarius, traversing the country from south to north. (See Cramer, Asia Minor, i. 167-215; Leake, Asia Minor, p. 306; Forbiger, Handbuch der Alten Geographie, vol. ii. p. 374, where all the ancient authorities referring to Bithynia are cited.)