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
Whatever could tell on a vain, unskilful, vacillating man--all the flattering arts of diplomacy, all the theatrical apparatus of patriotic enthusiasm--was put in motion to obtain the desired result; and--which was the main point--things had by the well-timed compliance of Crassus assumed such a shape, that Pompeius had no alternative but either to come forward openly as tyrant of Rome or to retire. So he at length yielded and consented to disband the troops. The command in the Mithradatic war, which he doubtless hoped to obtain when he had allowed himself to be chosen consul for 684, he could not now desire, since Lucullus seemed to have practically ended that war with the campaign of 683.
He deemed it beneath his dignity to accept the consular province assigned to him by the senate in accordance with the Sempronian law, and Crassus in this followed his example. Accordingly when Pompeius after discharging his soldiers resigned his consulship on the last day of 684, he retired for the time wholly from public affairs, and declared that he wished thenceforth to live a life of quiet leisure as a simple citizen. He had taken up such a position that he was obliged to grasp at the crown; and, seeing that he was not willing to do so, no part was left to him but the empty one of a candidate for a throne resigning his pretensions to it.
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Reference address : https://www.ellopos.net/elpenor/rome/5-03-fall-oligarchy-pompeius.asp?pg=20