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
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.
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.