Please note that Mommsen uses the AUC chronology (Ab Urbe Condita), i.e. from the founding of the City of Rome. You can use this reference table to have the B.C. dates
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
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. The far more wretched Asiatic militia, stationed farther back, thereupon gave themselves up as vanquished, even before they encountered the enemy; when the generals of Mithradates approached them, they dispersed.
A Roman division was defeated in Cappadocia; Cassius sought to keep the field in Phrygia with the militia, but he discharged it again without venturing on a battle, and threw himself with his few trustworthy troops into the townships on the upper Maeander, particularly into Apamea. Oppius in like manner evacuated Pamphylia and shut himself up in the Phrygian Laodicea; Aquillius was overtaken while retreating at the Sangarius in the Bithynian territory, and so totally defeated that he lost his camp and had to seek refuge at Pergamus in the Roman province; the latter also was soon overrun, and Pergamus itself fell into the hands of the king, as likewise the Bosporus and the ships that were there.
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Reference address : https://www.ellopos.net/elpenor/rome/4-08-east-king-mithradates.asp?pg=40