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
Rome, indeed, was not a mercantile city like Corinth or Carthage; for Latium was an essentially agricultural region, and Rome was in the first instance, and continued to be, pre-eminently a Latin city. But the distinction between Rome and the mass of the other Latin towns must certainly be traced back to its commercial position, and to the type of character produced by that position in its citizens. If Rome was the emporium of the Latin districts, we can readily understand how, along with and in addition to Latin husbandry, an urban life should have attained vigorous and rapid development there and thus have laid the foundation for its distinctive career.
It is far more important and more practicable to follow out the course of this mercantile and strategical growth of the city of Rome, than to attempt the useless task of chemically analysing the insignificant and but little diversified communities of primitive times. This urban development may still be so far recognized in the traditions regarding the successive circumvallations and fortifications of Rome, the formation of which necessarily kept pace with the growth of the Roman commonwealth in importance as a city.
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Reference address : https://www.ellopos.net/elpenor/rome/1-04-beginnings-rome.asp?pg=9