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
Besides, the formal retention of the earlier rates, while there was a general increase in the amount of men's means, involved of itself in some measure an extension of the suffrage in a democratic sense. The total number of the divisions remained likewise unchanged; but, while hitherto, as we have said, the 18 equestrian centuries and the 80 of the first class had, standing by themselves, the majority in the 193 voting centuries, in the reformed arrangement the votes of the first class were reduced to 70, with the result that under all circumstances at least the second grade came to vote.
Still more important, and indeed the real central element of the reform, was the connection into which the new voting divisions were brought with the tribal arrangement. Formerly the centuries originated from the tribes on the footing, that whoever belonged to a tribe had to be enrolled by the censor in one of the centuries. From the time that the non-freehold burgesses had been enrolled in the tribes, they too came thus into the centuries, and, while they were restricted in the -comitia tributa- to the four urban divisions, they had in the -comitia centuriata- formally the same right with the freehold burgesses, although probably the censorial arbitrary prerogative intervened in the composition of the centuries, and granted to the burgesses enrolled in the rural tribes the preponderance also in the centuriate assembly.
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Reference address : http://www.ellopos.net/elpenor/rome/3-11-government-governed.asp?pg=72