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
In regard however to this imposing republican equality we must not overlook the fact that it was to a considerable extent only formal, and that an aristocracy of a very decided stamp grew out of it or rather was contained in it from the very first. The non-patrician families of wealth and consideration had long ago separated from the plebs, and leagued themselves with the patriciate in the participation of senatorial rights and in the prosecution of a policy distinct from that of the plebs and very often counteracting it.
The Licinian laws abrogated the legal distinctions within the ranks of the aristocracy, and changed the character of the barrier which excluded the plebeian from the government, so that it was no longer a hindrance unalterable in law, but one, not indeed insurmountable, but yet difficult to be surmounted in practice. In both ways fresh blood was mingled with the ruling order in Rome; but in itself the government still remained, as before, aristocratic.
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Reference address : https://www.ellopos.net/elpenor/rome/2-03-equalization-orders-aristocracy.asp?pg=35