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
This was at the same time a declaration of war against Rome; therefore as soon as the revolt of the Jews was suppressed, Gabinius, the able and spirited governor of Syria, led the legions over the Euphrates. Meanwhile, however, a revolution had occurred in the Parthian empire; the grandees of the kingdom, with the young, bold, and talented grand vizier at their head, had overthrown king Mithradates and placed his brother Orodes on the throne. Mithradates therefore made common cause with the Romans and resorted to the camp of Gabinius. Everything promised the best results to the enterprise of the Roman governor, when he unexpectedly received orders to conduct the king of Egypt back by force of arms to Alexandria.(3)
3. Cf. V. IV. Ptolemaeus in Egypt Recognized, but Expelled by His Subjects
He was obliged to obey; but, in the expectation of soon coming back, he induced the dethroned Parthian prince who solicited aid from him to commence the war in the meanwhile at his own hand. Mithradates did so; and Seleucia and Babylon declared for him; but the vizier captured Seleucia by assault, having been in person the first to mount the battlements, and in Babylon Mithradates himself was forced by famine to surrender, whereupon he was by his brother's orders put to death. His death was a palpable loss to the Romans; but it by no means put an end to the ferment in the Parthian empire, and the Armenian war continued. Gabinius, after ending the Egyptian campaign, was just on the eve of turning to account the still favourable opportunity and resuming the interrupted Parthian war, when Crassus arrived in Syria and along with the command took up also the plans of his predecessor. Full of high-flown hopes he estimated the difficulties of the march as slight, and the power of resistance in the armies of the enemy as yet slighter; he not only spoke confidently of the subjugation of the Parthians, but was already in imagination the conqueror of the kingdoms of Bactria and India.
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Reference address : https://www.ellopos.net/elpenor/rome/5-09-crassus-joint-rulers.asp?pg=3