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
The aggregate effect of these measures was, that the senate wholly lost the power of control, and retained only so much of administration as the head of the state thought fit to leave to it. But these constitutive measures were not enough; the governing aristocracy for the time being was also directly assailed. It was a mere act of revenge, which assigned retrospective effect to the last-mentioned law and thereby compelled Publius Popillius--the aristocrat who after the death of Nasica, which had occurred in the interval, was chiefly obnoxious to the democrats--to go into exile.
It is remarkable that this proposal was only carried by 18 to 17 votes in the assembly of the tribes--a sign how much the influence of the aristocracy still availed with the multitude, at least in questions of a personal interest. A similar but far less justifiable decree--the proposal, directed against Marcus Octavius, that whoever had been deprived of his office by decree of the people should be for ever incapable of filling a public post--was recalled by Gaius at the request of his mother; and he was thus spared the disgrace of openly mocking justice by legalizing a notorious violation of the constitution, and of taking base vengeance on a man of honour, who had not spoken an angry word against Tiberius and had only acted constitutionally and in accordance with what he conceived to be his duty.
But of very different importance from these measures was the scheme of Gaius--which, it is true, was hardly carried into effect-- to strengthen the senate by 300 new members, that is, by just about as many as it hitherto had contained, and to have them elected from the equestrian order by the comitia--a creation of peers after the most comprehensive style, which would have reduced the senate into the most complete dependence on the chief of the state.
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Reference address : https://www.ellopos.net/elpenor/rome/4-03-revolution-gaius-gracchus.asp?pg=33