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
Like a crust of ice gathering imperceptibly over the surface of a stream and imperceptibly confining it more and more, this new Roman aristocracy silently arose; and not less imperceptibly, like the current concealing itself beneath and slowly extending, there arose in opposition to it the new party of progress.
It is very difficult to sum up in a general historical view the several, individually insignificant, traces of these two antagonistic movements, which do not for the present yield their historical product in any distinct actual catastrophe.
But the freedom hitherto enjoyed in the commonwealth was undermined, and the foundation for future revolutions was laid, during this epoch; and the delineation of these as well as of the development of Rome in general would remain imperfect, if we should fail to give some idea of the strength of that encrusting ice, of the growth of the current beneath, and of the fearful moaning and cracking that foretold the mighty breaking up which was at hand.
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Reference address : https://www.ellopos.net/elpenor/rome/3-11-government-governed.asp?pg=2