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
Less objectionable perhaps, but still not without hazard, was the arrangement by which the new allotments bore the character of heritable leaseholds and were inalienable. The most liberal principles in regard to freedom of dealing had made Rome great; and it was very little consonant to the spirit of the Roman institutions, that these new farmers were peremptorily bound down to cultivate their portions of land in a definite manner, and that their allotments were subject to rights of revocation and all the cramping measures associated with commercial restriction.
It will be granted that these objections to the Sempronian agrarian law were of no small weight. Yet they are not decisive. Such a practical eviction of the holders of the domains was certainly a great evil; yet it was the only means of checking, at least for a long time, an evil much greater still and in fact directly destructive to the state--the decline of the Italian farmer-class. We can well understand therefore why the most distinguished and patriotic men even of the conservative party, headed by Gaius Laelius and Scipio Aemilianus, approved and desired the distribution of the domains viewed in itself.
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Reference address : https://www.ellopos.net/elpenor/rome/4-02-reform-tiberius-gracchus.asp?pg=53