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 concentrated aspect assumed by the administration of finance showed itself first and most palpably in the treatment of the public lands, which tended almost directly to accomplish the material and moral annihilation of the middle classes. The use of the public pasture and of the state-domains generally was from its very nature a privilege of burgesses; formal law excluded the plebeian from the joint use of the common pasture.
As however, apart from the conversion of the public land into private property or its assignation, Roman law knew no fixed rights of usufruct on the part of individual burgesses to be respected like those of property, it depended solely on the pleasure of the king, so long as the public land remained such, to grant and to define its joint enjoyment; and it is not to be doubted that he frequently made use of his right, or at least his power, as to this matter in favour of plebeians.
But on the introduction of the republic the principle was again strictly insisted on, that the use of the common pasture belonged in law merely to the burgess of best right, or in other words to the patrician; and, though the senate still as before allowed exceptions in favour of the wealthy plebeian houses represented in it, the small plebeian landholders and the day-labourers, who stood most in need of the common pasture, had its joint enjoyment injuriously withheld from them.
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Reference address : https://www.ellopos.net/elpenor/rome/2-02-tribunate-plebs-decemvirate.asp?pg=4