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
On the tableland of Armenia, which lies 5000 feet and more above the level of the sea, the corn at Erzeroum only germinates in the beginning of June, and the winter sets in with the harvest in September; Artaxata had to be reached and the campaign had to be ended in four months at the utmost.
At midsummer, 686, Lucullus set out from Tigranocerta, and, marching doubtless through the pass of Bitlis and farther to the westward along the lake of Van--arrived on the plateau of Musch and at the Euphrates. The march went on--amidst constant and very troublesome skirmishing with the enemy's cavalry, and especially with the mounted archers--slowly, but without material hindrance; and the passage of the Euphrates, which was seriously defended by the Armenian cavalry, was secured by a successful engagement; the Armenian infantry showed itself, but the attempt to involve it in the conflict did not succeed.
Thus the army reached the tableland, properly so called, of Armenia, and continued its march into the unknown country. They had suffered no actual misfortune; but the mere inevitable delaying of the march by the difficulties of the ground and the horsemen of the enemy was itself a very serious disadvantage. Long before they had reached Artaxata, winter set in; and when the Italian soldiers saw snow and ice around them, the bow of military discipline that had been far too tightly stretched gave way.
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Reference address : https://www.ellopos.net/elpenor/rome/5-02-rule-sullan-restoration.asp?pg=55