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
But this war had in fact exposed the corruption of the government no less than it had revealed the utter nullity of the opposition. It was not possible to govern worse than the restoration governed in the years 637-645; it was not possible to stand forth more defenceless and forlorn than was the Roman senate in 645: had there been in Rome a real opposition, that is to say, a party which wished and urged a fundamental alteration of the constitution, it must necessarily have now made at least an attempt to overturn the restored senate.
No such attempt took place; the political question was converted into a personal one, the generals were changed, and one or two useless and unimportant people were banished. It was thus settled, that the so-called popular party as such neither could nor would govern; that only two forms of government were at all possible in Rome, a -tyrannis- or an oligarchy; that, so long as there happened to be nobody sufficiently well known, if not sufficiently important, to usurp the regency of the state, the worst mismanagement endangered at the most individual oligarchs, but never the oligarchy; that on the other hand, so soon as such a pretender appeared, nothing was easier than to shake the rotten curule chairs. In this respect the coming forward of Marius was significant, just because it was in itself so utterly unwarranted.
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Reference address : https://www.ellopos.net/elpenor/rome/4-04-rule-restoration.asp?pg=62