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 Duodecimal System
Otherwise generally in the case of those Italian measures, which were not connected with Greek standards and were probably developed by the Italians before they came into contact with the Greeks, there prevailed the partition of the "whole" (-as-) into twelve "units" (-unciae-). The very earliest Latin priesthoods, the colleges of the Salii and Arvales,(5) as well as the leagues of the Etruscan cities, were organized on the basis of the number twelve.
5. Cf. I. XII. Priests
The same number predominated in the Roman system of weights and in the measures of length, where the pound (-libra-) and the foot (-pes-) were usually subdivided into twelve parts; the unit of the Roman measures of surface was the "driving" (-actus-) of 120 square feet, a combination of the decimal and duodecimal systems.(6) Similar arrangements as to the measures of capacity may have passed into oblivion.
6. Originally both the -actus-, "riving," and its still more frequently occurring duplicate, the -jugerum-, "yoking," were, like the German "morgen," not measures of surface, but measures of labour; the latter denoting the day's work, the former the half-day's work, with reference to the sharp division of the day especially in Italy by the ploughman's rest at noon.
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Reference address : http://www.ellopos.net/elpenor/rome/1-14-measuring-writing.asp?pg=4