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
The latter, when he had arrived at the frontier of Armenia, was doomed to learn that the great-king Tigranes had set a price of 100 talents (24,000 pounds) on his head, had arrested his envoys, and had delivered them to the Romans. King Mithradates saw his kingdom in the hands of the enemy, and his allies on the point of coming to an agreement with them; it was not possible to continue the war; he might deem himself fortunate, if he succeeded in effecting his escape along the eastern and northern shores of the Black Sea, in perhaps dislodging his son Machares--who had revolted and entered into connection with the Romans(6)--once more from the Bosporan kingdom, and in finding on the Maeotis a fresh soil for fresh projects.
6. Cf. V. II. Sieges of the Pontic Cities
So he turned northward. When the king in his flight had crossed the Phasis, the ancient boundary of Asia Minor, Pompeius for the time discontinued his pursuit; but instead of returning to the region of the sources of the Euphrates, he turned aside into the region of the Araxes to settle matters with Tigranes.
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Reference address : https://www.ellopos.net/elpenor/rome/5-04-pompeius-east.asp?pg=15