No unity of military organization, it is true, bound together these party-coloured masses; the army of Mithradates was just one of those unwieldy Asiatic war-machines, which had so often already--on the last occasion exactly a century before at Magnesia-- succumbed to a superior military organization; but still the east was in arms against the Romans, while in the western half of the empire also matters looked far from peaceful.
Weak Counterpreparatons of the Romans However much it was in itself a political necessity for Rome to declare war against Mithradates, yet the particular moment was as unhappily chosen as possible; and for this reason it is very probable that Manius Aquillius brought about the rupture between Rome and Mithradates at this precise time primarily from regard to his own interests.

For the moment they had no other troops at their disposal in Asia than the small Roman division under Lucius Cassius and the militia of western Asia, and, owing to the military and financial distress in which they were placed at home in consequence of the insurrectionary war, a Roman army could not in the most favourable case land in Asia before the summer of 666.

Hitherto the Roman magistrates there had a difficult position; but they hoped to protect the Roman province and to be able to hold their ground as they stood--the Bithynian army under king Nicomedes in its position taken up in the previous year in the Paphlagonian territory between Amastris and Sinope, and the divisions under Lucius Cassius, Manius Aquillius, and Quintus Oppius, farther back in the Bithynian, Galatian, and Cappadocian territories, while the Bithyno-Roman fleet continued to blockade the Bosporus.
Mithradates Occupies Asia Minor Anti-Roman Movements There In the beginning of the spring of 666 Mithradates assumed the offensive.

On a tributary of the Halys, the Amnias (near the modern Tesch Kopri), the Pontic vanguard of cavalry and light-armed troops encountered the Bithynian army, and notwithstanding its very superior numbers so broke it at the first onset that the beaten army dispersed and the camp and military chest fell into the hands of the victors.

It was mainly to Neoptolemus and Archelaus that the king was indebted for this brilliant success.