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
Moreover there had hitherto been paid for the cattle driven out on the common pasture a grazing-tax, which was moderate enough to make the right of using that pasture still be regarded as a privilege, and yet yielded no inconsiderable revenue to the public purse. The patrician quaestors were now remiss and indulgent in levying it, and gradually allowed it to fall into desuetude.
Hitherto, particularly when new domains were acquired by conquest, allocations of land had been regularly arranged, in which all the poorer burgesses and μέτοικοι were provided for; it was only the land which was not suitable for agriculture that was annexed to the common pasture.
The ruling class did not venture wholly to give up such assignations, and still less to propose them merely in favour of the rich; but they became fewer and scantier, and were replaced by the pernicious system of occupation-that is to say, the cession of domain-lands, not in property or under formal lease for a definite term, but in special usufruct until further notice, to the first occupant and his heirs-at-law, so that the state was at any time entitled to resume them, and the occupier had to pay the tenth sheaf, or in oil and wine the fifth part of the produce, to the exchequer.
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Reference address : https://www.ellopos.net/elpenor/rome/2-02-tribunate-plebs-decemvirate.asp?pg=5