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
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.
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Reference address : https://www.ellopos.net/elpenor/rome/5-02-rule-sullan-restoration.asp?pg=46