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
Clearly as the defects of the Roman aristocracy were apparent, and decidedly as the steady growth of aristocratic ascendency was connected with the practical setting aside of the tribunate, none can fail to see that government could not be long carried on with an authority which was not only aimless and virtually calculated to put off the suffering proletariate with a deceitful prospect of relief, but was at the same time decidedly revolutionary and possessed of a--strictly speaking --anarchical prerogative of obstruction to the authority of the magistrates and even of the state itself.
But that faith in an ideal, which is the foundation of all the power and of all the impotence of democracy, had come to be closely associated in the minds of the Romans with the tribunate of the plebs; and we do not need to recall the case of Cola Rienzi in order to perceive that, however unsubstantial might be the advantage thence arising to the multitude, it could not be abolished without a formidable convulsion of the state.
Accordingly with genuine political prudence they contented themselves with reducing it to a nullity under forms that should attract as little attention as possible. The mere name of this essentially revolutionary magistracy was still retained within the aristocratically governed commonwealth--an incongruity for the present, and for the future, in the hands of a coming revolutionary party, a sharp and dangerous weapon.
For the moment, however, and for a long time to come the aristocracy was so absolutely powerful and so completely possessed control over the tribunate, that no trace at all is to be met with of a collegiate opposition on the part of the tribunes to the senate; and the government overcame the forlorn movements of opposition that now and then proceeded from individual tribunes, always without difficulty, and ordinarily by means of the tribunate itself.
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Reference address : https://www.ellopos.net/elpenor/rome/2-03-equalization-orders-aristocracy.asp?pg=53