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
But where the man who had twice led the Roman army from deep decline to victory despaired, a youth without achievements had the boldness to give himself forth as the saviour of Italy. He was called Tiberius Sempronius Gracchus (591-621). His father who bore the same name (consul in 577, 591; censor in 585), was the true model of a Roman aristocrat. The brilliant magnificence of his aedilician games, not produced without oppressing the dependent communities, had drawn upon him the severe and deserved censure of the senate;(24)
24. Cf. III. XI. Position of the Governors
his interference in the pitiful process directed against the Scipios who were personally hostile to him(25) gave proof of his chivalrous feeling, and perhaps of his regard for his own order; and his energetic action against the freedmen in his censorship(26) evinced his conservative disposition.
25. Cf. III. IX. Death of Scipio
26. Cf. III. XI. Reform of the Centuries
As governor, moreover, of the province of the Ebro,(27) by his bravery and above all by his integrity he rendered a permanent service to his country, and at the same time raised to himself in the hearts of the subject nation an enduring monument of reverence and affection.
27. Cf. III. VII. Gracchus
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Reference address : https://www.ellopos.net/elpenor/rome/4-02-reform-tiberius-gracchus.asp?pg=34