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
If Pompeius acknowledged the oligarchic constitution and offered to fight for it against Caesar, the republican opposition might and must recognize him as its general, and in alliance with him compel the timid majority to a declaration of war. That Pompeius was not quite in earnest with his fidelity to the constitution, could indeed escape nobody; but, undecided as he was in everything, he had by no means arrived like Caesar at a clear and firm conviction that it must be the first business of the new monarch to sweep off thoroughly and conclusively the oligarchic lumber.
At any rate the war would train a really republican army and really republican generals; and, after the victory over Caesar, they might proceed with more favourable prospects to set aside not merely oneof the monarchs, but the monarchy itself, which was in the course of formation. Desperate as was the cause of the oligarchy, the offer of Pompeius to become its ally was the most favourable arrangement possible for it.
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Reference address : https://www.ellopos.net/elpenor/rome/5-09-crassus-joint-rulers.asp?pg=29