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
Early Urban Character of Rome
But in connection with this view of the position of Rome as the emporium of Latium another observation suggests itself. At the time when history begins to dawn on us, Rome appears, in contradistinction to the league of the Latin communities, as a compact urban unity. The Latin habit of dwelling in open villages, and of using the common stronghold only for festivals and assemblies or in case of special need, was subjected to restriction at a far earlier period, probably, in the canton of Rome than anywhere else in Latium. The Roman did not cease to manage his farm in person, or to regard it as his proper home; but the unwholesome atmosphere of the Campagna could not but induce him to take up his abode as much as possible on the more airy and salubrious city hills; and by the side of the cultivators of the soil there must have been a numerous non-agricultural population, partly foreigners, partly native, settled there from very early times.
This to some extent accounts for the dense population of the old Roman territory, which may be estimated at the utmost at 115 square miles, partly of marshy or sandy soil, and which, even under the earliest constitution of the city, furnished a force of 3300 freemen; so that it must have numbered at least 10,000 free inhabitants. But further, every one acquainted with the Romans and their history is aware that it is their urban and mercantile character which forms the basis of whatever is peculiar in their public and private life, and that the distinction between them and the other Latins and Italians in general is pre-eminently the distinction between citizen and rustic.
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Reference address : https://www.ellopos.net/elpenor/rome/1-04-beginnings-rome.asp?pg=8