Next in importance to Nicomedeia and Nicaea was Prusias. Its reputed founder was Prusias I, the fourth king of Bithynia, but there was also a tradition which attributed its founding to Hannibal. Of all the cities on the western seaboard none had a more beautiful situation. Built on a low spur which projects to the northeast from the Mysian Mt. Olympus, it faces a rich and well-watered plain. On a flat-topped rock at its back rises the acropolis, perhaps the site of the original city, and behind this towers the majestic mass of Olympus. Forest covers its lower slopes, while its higher peaks -- one of them 8,000 feet above sea-level -- are capped with eternal snow. Under the later Bithynian kings Prusias seems to have had a Council vested with power for local administration, but the place was regarded throughout Antiquity as a small city. Among its chief assets were sulphur and other thermal springs, rising on the mountain-side west of the city, which appear to have made Prusias a centre for medical treatment; they remain to this day a source of considerable wealth.

In the mountainous portion of Bithynia that lies east of the Sangarius were two places of importance: a second Prusias, distinguished from the coast city by the name of Prusias-on-the-Hypius, and Bithynium. Bithynium was the most easterly of the cities of the kingdom and on the great road leading to Pontus. The remains of a wall of polygonal masonry which surrounded its acropolis show that the place was an early settlement. The well-irrigated plain and also the lower slopes of the neighbouring mountains afforded excellent pasturage for cattle, and the cheese produced in the plain of Salona won particular fame. Another asset of commercial value may have been the nearby thermal springs which are still much frequented.

The Kingdom of Bithynia was founded amid the general confusion which followed the death of Antigonus in 301. Zipoetes, a local “dynast” whose ancestors for at least three generations had wielded some sort of power in the country, defeated Lysimachus and his generals in a series of battles and assumed the title of King. He enlarged his dominions by seizing part of the territory of Heracleia, and defended himself successfully against an attack from Antiochus I of Syria, thus establishing his power over Bithynia.

From the same book , pp. 306-311