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
But while the Armenians were still forming their array, the quick
eye of Lucullus perceived that they had neglected to occupy a height
which commanded the whole position of their cavalry. He hastened
to occupy it with two cohorts, while at the same time his weak
cavalry by a flank attack diverted the attention of the enemy
from this movement; and as soon as he had reached the height, he led
his little band against the rear of the enemy's cavalry. They were
totally broken and threw themselves on the not yet fully formed
infantry, which fled without even striking a blow.
The bulletin
of the victor--that 100,000 Armenians and five Romans had fallen
and that the king, throwing away his turban and diadem, had galloped
off unrecognized with a few horsemen--is composed in the style
of his master Sulla. Nevertheless the victory achieved on the 6th
October 685 before Tigranocerta remains one of the most brilliant
stars in the glorious history of Roman warfare; and it was not less
momentous than brilliant.