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
Difficulties to Be Encountered
The resolution was a grave one, especially considering the condition of the Roman army. It was indispensable during the campaign in Armenia to keep the extensive territory of Pontus strongly occupied, for otherwise the army stationed in Armenia might lose its communications with home; and besides it might be easily foreseen that Mithradates would attempt an inroad into his former kingdom. The army, at the head of which Lucullus had ended the Mithradatic war, amounting to about 30,000 men, was obviously inadequate for this double task.
Under ordinary circumstances the general would have asked and obtained from his government the despatch of a second army; but as Lucullus wished, and was in some measure compelled, to take up the war over the head of the government, he found himself necessitated to renounce that plan and--although he himself incorporated the captured Thracian mercenaries of the Pontic king with his troops--to carry the war over the Euphrates with not more than two legions, or at most 15,000 men.
This was in itself hazardous; but the smallness of the number might be in some degree compensated by the tried valour of the army consisting throughout of veterans. A far worse feature was the temper of the soldiers, to which Lucullus, in his high aristocratic fashion, had given far too little heed. Lucullus was an able general, and--according to the aristocratic standard-- an upright and kindly-disposed man, but very far from being a favourite with his soldiers.
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Reference address : https://www.ellopos.net/elpenor/rome/5-02-rule-sullan-restoration.asp?pg=41