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 Commisssion for Distributing the Domains
Tiberius Gracchus was dead; but his two works, the distribution of land and the revolution, survived their author. In presence of the starving agricultural proletariate the senate might venture on a murder, but it could not make use of that murder to annul the Sempronian agrarian law; the law itself had been far more strengthened than shaken by the frantic outbreak of party fury.
The party of the aristocracy friendly towards reform, which openly favoured the distribution of the domains--headed by Quintus Metellus, just about this time (623) censor, and Publius Scaevola--in concert with the party of Scipio Aemilianus, which was at least not disinclined to reform, gained the upper hand for the time being even in the senate; and a decree of the senate expressly directed the triumvirs to begin their labours.
According to the Sempronian law these were to be nominated annually by the community, and this was probably done: but from the nature of their task it was natural that the election should fall again and again on the same men, and new elections in the proper sense occurred only when a place became vacant through death.
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