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
Union of the Plebians
The tribunician movements appear to have mainly originated in social rather than political discontent, and there is good reason to suppose that some of the wealthy plebeians admitted to the senate were no less opposed to these movements than the patricians. For they too benefited by the privileges against which the agitation was mainly directed; and although in other respects they found themselves treated as inferior, it probably seemed to them by no means an appropriate time for asserting their claim to participate in the magistracies, when the exclusive financial power of the whole senate was assailed. This explains why during the first fifty years of the republic no step was taken aiming directly at the political equalization of the orders.
But this league between the patricians and the wealthy plebeians by no means bore within itself any guarantee of permanence. Beyond doubt from the very first a portion of the leading plebeian families had attached themselves to the movement-party, partly from a sense of what was due to the fellow-members of their order, partly in consequence of the natural bond which unites all who are treated as inferior, and partly because they perceived that concessions to the multitude were inevitable in the issue, and that, if turned to due account, they would result in the abrogation of the exclusive rights of the patriciate and would thereby give to the plebeian aristocracy a decisive preponderance in the state.
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Reference address : https://www.ellopos.net/elpenor/rome/2-03-equalization-orders-aristocracy.asp