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
This order of the equites--that is to say, substantially, of the wealthy merchants--in various ways came roughly into contact with the governing senate. There was a natural antipathy between the genteel aristocrats and the men to whom money had brought rank.
The ruling lords, especially the better class of them, stood just as much aloof from speculations, as the men of material interests were indifferent to political questions and coterie-feuds. The two classes had already frequently come into sharp collision, particularly in the provinces; for, though in general the provincials had far more reason than the Roman capitalists had to complain of the partiality of the Roman magistrates, yet the ruling lords of the senate did not lend countenance to the greedy and unjust doings of the moneyed men, at the expense of the subjects, so thoroughly and absolutely as those capitalists desired.
In spite of their concord in opposing a common foe such as was Tiberius Gracchus, a deep gulf lay between the nobility and the moneyed aristocracy; and Gaius, more adroit than his brother, enlarged it till the alliance was broken up and the mercantile class ranged itself on his side.
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Reference address : https://www.ellopos.net/elpenor/rome/4-03-revolution-gaius-gracchus.asp?pg=26