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
Subdivision of the Magistracy - Censorship
Moreover they broke up the supreme power which had hitherto been undivided, in order to delay their inevitable defeat by multiplying the points to be assailed. Thus the adjustment of the budget and of the burgess--and taxation-rolls, which ordinarily took place every fourth year and had hitherto been managed by the consuls, was entrusted as early as the year 319 to two valuators (-censores-), nominated by the centuries from among the nobles for a period, at the most, of eighteen months.
The new office gradually became the palladium of the aristocratic party, not so much on account of its financial influence as on account of the right annexed to it of filling up the vacancies in the senate and in the equites, and of removing individuals from the lists of the senate, equites, and burgesses on occasion of their adjustment. At this epoch, however, the censorship by no means possessed the great importance and moral supremacy which afterwards were associated with it.
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Reference address : http://www.ellopos.net/elpenor/rome/2-03-equalization-orders-aristocracy.asp?pg=8