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 treaty of peace which Mancinus concluded with the Numantines in 617, was in substance the work of Gracchus;(29) the recollection that the senate had cancelled it, that the general had been on its account surrendered to the enemy, and that Gracchus with the other superior officers had only escaped a like fate through the greater favour which he enjoyed among the burgesses, could not put the young, upright, and proud man in better humour with the ruling aristocracy.
29. Cf. IV. I. Mancinus
The Greek rhetoricians with whom he was fond of discussing philosophy and politics, Diophanes of Mytilene and Gaius Blossius of Cumae, nourished within his soul the ideals over which he brooded: when his intentions became known in wider circles, there was no want of approving voices, and many a public placard summoned the grandson of Africanus to think of the poor people and the deliverance of Italy.
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Reference address : https://www.ellopos.net/elpenor/rome/4-02-reform-tiberius-gracchus.asp?pg=37