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
Political Value of the Tribunate
But what was gained by a measure which broke up the unity of the state; which subjected the magistrates to a controlling authority unsteady in its action and dependent on all the passions of the moment; which in the hour of peril might have brought the administration to a dead-lock at the bidding of any one of the opposition chiefs elevated to the rival throne; and which, by investing all the magistrates with co-ordinate jurisdiction in the administration of criminal law, as it were formally transferred that administration from the domain of law to that of politics and corrupted it for all time coming?
It is true indeed that the tribunate, if it did not directly contribute to the political equalization of the orders, served as a powerful weapon in the hands of the plebeians when these soon afterwards desired admission to the offices of state. But this was not the real design of the tribunate. It was a concession wrung not from the politically privileged order, but from the rich landlords and capitalists; it was designed to ensure to the commons equitable administration of law, and to promote a more judicious administration of finance.
This design it did not, and could not, fulfil. The tribune might put a stop to particular iniquities, to individual instances of crying hardship; but the fault lay not in the unfair working of a righteous law, but in a law which was itself unrighteous, and how could the tribune regularly obstruct the ordinary course of justice? Could he have done so, it would have served little to remedy the evil, unless the sources of impoverishment were stopped--the perverse taxation, the wretched system of credit, and the pernicious occupation of the domain-lands. But such measures were not attempted, evidently because the wealthy plebeians themselves had no less interest in these abuses than the patricians.
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Reference address : https://www.ellopos.net/elpenor/rome/2-02-tribunate-plebs-decemvirate.asp?pg=21