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
Difficulty with the Parthians
Far more fraught with momentous effects than these new relations of the Romans to the Armenians, Iberians, Bosporans, and Nabataeans was the proximity into which through the occupation of Syria they were brought with the Parthian state. Complaisant as had been the demeanour of Roman diplomacy towards Phraates while the Pontic and Armenian states still subsisted, willingly as both Lucullus and Pompeius had then conceded to him the possession of the regions beyond the Euphrates,(19) the new neighbour now sternly took up his position by the side of the Arsacids; and Phraates, if the royal art of forgetting his own faults allowed him, might well recall now the warning words of Mithradates that the Parthian by his alliance with the Occidentals against the kingdoms of kindred race paved the way first for their destruction and then for his own.
19. Cf. V. II. Renewal of the War, V. IV. Variance between Mithradates and Tigranes
Romans and Parthians in league had brought Armenia to ruin; when it was overthrown, Rome true to her old policy now reversed the parts and favoured the humbled foe at the expense of the powerful ally. The singular preference, which the father Tigranes experienced from Pompeius as contrasted with his son the ally and son-in-law of the Parthian king, was already part of this policy; it was a direct offence, when soon afterwards by the orders of Pompeius the younger Tigranes and his family were arrested and were not released even on Phraates interceding with the friendly general for his daughter and his son-in-law.
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Reference address : https://www.ellopos.net/elpenor/rome/5-04-pompeius-east.asp?pg=46