Bithynia is an ancient country of north-west Asia Minor, in present-day Turkey. The original inhabitants were Thracians who established themselves as independent and were given some autonomy after Cyrus the Great incorporated Bithynia into the Persian Empire. After the death of Alexander the Great, the Bithynians took advantage of the wars of the Diadochi to secure freedom from the Seleucids (297 B.C.). They established a dynasty under the leadership of Zipoetes who was succeeded (c. 280 B.C.) by Nicomedes I, who founded Nicomedia as the capital of his flourishing state. During his time and the following reigns of Prusias I, Prusias II, and Nicomedes II, wars continued with the Seleucids and with Pergamum. In the 1st cent. B.C., Mithradates VI of Pontus had designs on Bithynia, which was ruled by Nicomedes IV (sometimes confused with Nicomedes III), a client of Rome. When Nicomedes died (74 B.C.) he willed Bithynia to Rome.
c. 294 BC: Ziboetes recognised as king
c. 279-255 BC: Nicomedes I
c. 255- 228: Ziaelas
228- 185: Prusias I
185-149: Prusias II
149-128: Nicomedes II Epiphanes (the god manifest)
128- 94: Nicomedes III Euergetes
94- 74: Nicomedes IV
75: Becomes a Roman Province.

"The Greeks think that the Thracians who marched to the Trojan war with Rhesus, who was killed by Diomedes in the night-time in the manner described in Homer’s poems, (1) fled to the outlet of the Euxine sea at the place where the crossing to Thrace is shortest. Some say that as they found no ships they remained there and possessed themselves of the country called Bebrycia. Others say that they crossed over to the country beyond Byzantium called Thracian Bithynia and settled along the river Bithya, but were forced by hunger to return to Bebrycia, to which they gave the name of Bithynia from the river where they had previously dwelt; or perhaps the name was changed by them insensibly with the lapse of time, as there is not much difference between Bithynia and Bebrycia. So some think. Others say that their first ruler was Bithys, the son of Zeus and Thrace, and that the two countries received their names from them.
So much by way of preface concerning Bithynia. Of the forty-nine kings who successively ruled the country before the Romans, the one most worthy of my mention, in writing Roman history, is Prusias, surnamed the Hunter..." (2)
The exact origin of the Bithynians may be obscure but the sources agree with Appian that they were Thracians. Bevan, for instance, says they were "Thracian immigrants from the opposite shore, and shared the same characteristics as their European cousins, savage hardihood, wild abandonment to the frenzy of religion and war. The terror of them kept the Greeks from making any settlement along their coast, from Calchedon to Heraclea, and woe betide the mariner driven to land there!" (3)
It was perhaps these characteristics that enabled the Bithynians to remain more-or-less independent until 75 B.C. , when ,the kingdom was bequeathed to Rome by Prusias’ grandson. Duncan Head (4) says they were practically independent of Persia from 435 B.C. However, Bevan (5) says that the Persian subjection of Asia Minor was very incomplete: the arm of the central government never reached far from the highroads. The Bithynians were always causing trouble to Hellespontine Phrygia, the satrapy to which they nominally belonged. Pharnabazus allied with them against a common foe (the Ten Thousand) in 400 B.C., but was glad enough to see the Greeks wintering in their territory two years later, "as the Bithynians were constantly making war against him." (6)
During the latter part of the fifth century, a chief called Doedalsus began the unification of the Bithynians. He became the founder of the Bithynian dynasty. His grandson, Bas, defeated a well-equipped force that had been marched into Bithynia by Calas, Alexander’s satrap of Hellespontine Phrygia. Alexander hadn’t marched through Bithynia, and subjection of the area was left to his commanders. This they failed to do.
Ziboetes, son of Bas, besieged Astacus and Calchedon in 315. Polemaeus, Antigonus’ general stopped him, but was obliged to make some bargain with Ziboetes, which was embodied in an alliance (7). Ziboetes would later found the city of Ziboetium, under Mount Lypedrum. Though the location of this city is uncertain, it is a sign of increasing Hellenisation.
Between the battles of Ipsus (301 B.C.) and Corupedion (281 B.C.), Bithynia was allocated to Lysimachus. He sent two armies in succession against Ziboetes, who defeated both. Then Lysimachus marched in person, only to be defeated again. He was prevented by his death at Corupedion from making any further attempts to subjugate the area. In 297, Ziboetes declared himself king.
After Corupedion, the principality was ostensibly part of Selucus’ domain. However, Selucus was more concerned with conquering Thrace, and hadn’t taken any significant action against Bithynia when he was assasinated seven months later. Selucus’ successor, Antiochus I, sent a force under Hermogenes against Heraclea. and the Bithynians. As Bevan says "the sight of Macedonian armies fleeing down the valleys before the tribesmen was almost familiar in Bithynia." Ziboetes was apon Hermogenes before the latter knew it, and the Selucids sent packing.
Shortly after, Ziboetes died, leaving his realm to his eldest son. Nicomedes I. Nicomedes had tried to kill all his brothers, but one, called Ziboetes, survived. He took control of north-west Bithynia. Nicomedes ceded his brother’s domain to Heraclea, and allied himself with Antigonus Gonatas (King of Macedon) and Heraclea against Antiochus. Ziboetes was defeated in the battle that followed, but continued to rule part of the country.
At this point (277 BC) the Gauls appeared on the European shore of the Hellespont, eager to cross over to Asia. Nicomedes made a treaty with them, in which they were placed under his orders. Then they were allowed to cross, and were unleashed upon Ziboetes, who probably died soon after. However, Nicomedes wasn’t able to retain control of the Galatians, and they were soon roaming around Phrygia, plundering and destroying. However, this had the fortunate effect of keeping Antiochus and his successors busy. No other attempt at conquest of Bithynia was made by the Selucid overlord.
Under Nicomedes I, the kingdom became hellenised. It began to have its own coinage. In 264, Nicomedia was founded on the opposite shore from the former site of Astacus, a city demolished by Lysimachus. The former Astacan citizens were settled there. It was still a major city during the Byzantine era.
About 250 B.C.. Nicomedes died. His wife, Etazeta, continued to rule on behalf of their infant sons. Zialas, a grown-up son by an earlier wife, Ditizele, had previously fled to Armenia. Now Ziaelas returned, at the head of some Galatians. Although Etazeta was supported by neighbouring cities and Antigonus, Ziaelas conquered first part, then all of Bithynia. Etazeta and her sons, including another Ziboetes, fled to Antigonus’ court in Macedonia. Around 235 B.C., Ziaelas was murdered by some of his Galatians, leaving his son Prusias I on the throne.
Like his father, Prusias was mainly concerned with playing off rival claimants for the Selucid diadem against each other. and against the rising power of Pergamon. The last was Bithynia’s main contender for power in the region, and the two states were often at war. In 216, some Gauls who had been brought over from Europe by Attalus of Pergamon began terrorising the area around Abydus. Prusias led an army against them, and destroyed all the men in a pitched battle (8). Attalus had been fighting Achaeus, a claimant to the Selucid throne. In 219 Prusias allied with Achaeus and Rhodes to stop Byzantium from levying tolls on passing ships. He hired the local Thracians to keep the Byzantines inside the city. Byzantium countered by encouraging Ziboetes to come out of exile in Macedon and take his rightful inheritance. Ziboetes died on the way, though, and Byzantium was compelled to make peace. (9)
This peace, concluded in a hurry for fear of Ziboetes, required Prusias to give up his conquests in Mysia. He regained the area later, though. For the 2nd Macedonian War, in 197, he was the "friend and ally" of Philip V of Macedon, who sent Prusias help in the destruction of Cios (10). Five years later, Bithynia was aligned With Antiochus III in his war against Rome and Pergamon. However, after Antiochus was thrown out of Greece, the Romans persuaded Prusias to switch sides. At the peace of Apamea (110 B.C.), Eumenes (of Pergamon) complained that Bithynia had taken Mysia from him, and Prusias was forced to give it up. However, he was allowed to keep the rest of his realm. (11)
In 186, he sought to challenge this settlement, by taking Hannibal into his employ, and attacking Eumenes. Hannibal won a naval victory, but the three year war went mostly against Prusias. Titus Flaminius was sent to Bithynia to end the war, and Hannibal. committed suicide while under house arrest. Shortly after, Bithynia was allied with Pergamon and Ariathres of Cappodocia against Pharnaces of Pontus and Mithridates of Armenia. The latter two were defeated in 179, but by then Prusias had died, and been succeeded by his son, Prusias II "the Hunter".
Excerpts from: http://members.nbci.com/_XMCM/thrace/bithynia_main.htm
NOTES
o Homer, Homer, Iliad X, 482-497
o Appian, Mithridatic Wars, 1 (Loeb Trans.)
o Bevan Vol 1, p81; Xenophon, Anabasis VI,4,1
o D. Head, Armies and Enemies of the Macedonian and Punic Wars, p 29
o Bevan, Vol 1, p 78
o Xenophon, Hellenica, 11,2; Anabasis p283 (Penguin)
o Bevan Vol 1, p 96
o Polybius V, 111
o Polybius IV, 51-52
o Livy XXXII, 35
o Livy XXXVI, 56
o Livy XLIV, 15; XLV, 44
o Appian, Mithridatic Wars, 1, 4
o Appian, ibid, 111, 17
o D. Head, ibid
o Bevan, Vol 1, Appendix G
o Appian, ibid.

BIBLIOGRAPHY
E.R. Bevan, The House of Seleucus, Routledge & Kegan Paul, London, 1966
Livy, Rome and the Mediterranean, Penguin
Xenophon, Hellenica , Penguin
Xenophon, Anabasis, Penguin
Appian, The Mithridatic Wars’, Loeb
Polybius, Histories, Loeb
A. R. Burn, The Pelican History of Greece, Penguin, 1982
D. Head, Armies of the Macedonian and Punic Wars, W.R.G., 1982
J. Warry, Warfare in The Classical World, Salamander, 1980
N Davis & C M Kraay, The Hellenistic Kingdoms, Thames & Hudson, London,1973
Duncan Head, The Achaemenid Persian Army, Montvert Publications, Stockport, 1992.