The main basis for this article is the body of funerary stelai from within Bithynia and its periphery. Almost all of these stelai date to the second century BC, with the remaining few dating to the first century BC. Despite the lack of variety in sources, a plethora of information can be gleaned from these stelai, allowing us to illuminate a relatively obscure army from the late Hellenistic period, providing details of the equipment and social conditions of the cavalry, infantry, and even the naval force of the Bithynians.

Xenophon, in his Anabasis, provides us with one of the first detailed accounts of Bithynia:

The place which goes by the name of Calpe Haven is in Asiatic Thrace, the name given to a region extending from the mouth of the Euxine all the way to Heraclea, which lies on the right hand as you sail into the Euxine. It is a long day's voyage for a war-ship, using her three banks of oars, from Byzantium to Heraclea, and between these two there is not a single Hellenic or friendly city, but only these Bithynian Thracians, who have a bad reputation for the savagery with which they treat any Greeks cast ashore by shipwreck or otherwise thrown into their power.

The natives of Bithynia, at least as far back as Herodotus, were known to be Thracians who had migrated across the Bosporus from Europe. When this migration took place is unknown. The land is often called “Asian Thrace” and the people the “Thracians of Asia.” In Xenophon’s day, the Bithynians were considered a backward and thoroughly uncivilized people only really notable for their malignancy towards those who became stranded in their territory. By the fall of Lysimachus in 281 BC, the kingdom of Bithynia had become an independent political force in western Asia Minor, though not a particularly large or powerful one in the scope of the Hellenistic world. It extended from the western shores of the Sea of Marmara to, at its farthest eastern reaches, the major Greek city of Heraclea Pontica (a city which it never controlled). Its main territory lay around the river Sangarius, its fertile valley, and the hilly lands beside it. The country of Bithynia provided amply for its inhabitants, with vast forests, quarries, grain fields, and pastures. Before the invasion of Alexander, this region of Asia Minor had been associated with the satrapy of Dascyleum in the Persian kingdom.

From the end of the fourth century, Bithynia grew from a small, isolated kingdom into prominent minor kingdom. In 297 BC, when Zipoites became the first Bithynian ruler to assume the title of king, Bithynia was still removed from major access to the sea and, thus, major Pontic or Aegean trade. He laid the foundation for the future Bithynian state when he first put into motion a process of modernization that included establishing Greek cities. It was Nicomedes I, though, who first began in earnest what could be deemed a program of hellenization in Bithynia. Ascending to the throne in 280, he moved the capital to the coast in 264. This new capital, Nicomedea, was a major urban centre, inhabited by Greeks, and cleverly established to fill the void left in the eastern Sea of Marmara by the destruction of Astacus earlier in the third century. Nicomedes also began to donate to the cities of Greece in an effort to secure his image as an important Hellenistic king. His son Ziaelas continued this program after becoming king, as did the next king Prusias I, founding several poleis named after the Bithynian royal family in the Macedonian fashion (a habit initiated by Zipoites and his founding of Zipoitum).

The Bithynian military has been dealt with fleetingly in the past. Griffith covered it in The Mercenaries of the Hellenistic and wrote:

...[I]t would be surprising if we were to find that [Bithynia] developed anything in the nature of an Hellenistic military system such as has been described in connection with the Ptolemaic and Seleucid empires, or even that of Pergamum: and no trace in fact of any such development exists.... [T]here is nothing to make one think that they kept standing armies of mercenaries, much less were able to command a supply of Greeks from military settlements like those of the Seleucids, and in the absence of further evidence it seems more probable that their standing armies must have consisted of soldiers drawn from their own subjects, after the old Persian system.

Rostovtzeff echoed this in his coverage, in the absolute briefest sense, of the Bithynian army in Social and Economic History of the Hellenistic World:

[We do not have] any idea to what extent the Bithynians adopted the Hellenistic military policy of their neighbours, the system of mercenary soldiers and military katoikoi. Their armies appear to have been recruited from their own subjects, reinforced by Galatian mercenaries.

A consideration of more recent evidence, namely a number of stelai and some other useful sources, provides us with a more comprehensive image of this minor Hellenistic kingdom’s military. These stelai give us a good idea of the weaponry and equipment of the soldiers fighting in the Bithynian army during the second century against Pergamum, Pontus, and Cappadocia.