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
Earliest Limits of the Roman Territory
Let us notice first of all the earliest boundaries of the Roman territory. Towards the east the towns of Antemnae, Fidenae, Caenina, and Gabii lie in the immediate neighbourhood, some of them not five miles distant from the Servian ring-wall; and the boundary of the canton must have been in the close vicinity of the city gates. On the south we find at a distance of fourteen miles the powerful communities of Tusculum and Alba; and the Roman territory appears not to have extended in this direction beyond the -Fossa Cluilia-, five miles from Rome. In like manner, towards the south-west, the boundary betwixt Rome and Lavinium was at the sixth milestone. While in a landward direction the Roman canton was thus everywhere confined within the narrowest possible limits, from the earliest times, on the other hand, it extended without hindrance on both banks of the Tiber towards the sea.
Between Rome and the coast there occurs no locality that is mentioned as an ancient canton-centre, and no trace of any ancient canton-boundary. The legend indeed, which has its definite explanation of the origin of everything, professes to tell us that the Roman possessions on the right bank of the Tiber, the "seven hamlets" (-septem pagi-), and the important salt-works at its mouth, were taken by king Romulus from the Veientes, and that king Ancus fortified on the right bank the -tete de pont-, the "mount of Janus" (-Janiculum-), and founded on the left the Roman Peiraeus, the seaport at the river's "mouth" (-Ostia-). But in fact we have evidence more trustworthy than that of legend, that the possessions on the Etruscan bank of the Tiber must have belonged to the original territory of Rome; for in this very quarter, at the fourth milestone on the later road to the port, lay the grove of the creative goddess (-Dea Dia-), the primitive chief seat of the Arval festival and Arval brotherhood of Rome.
Indeed from time immemorial the clan of the Romilii, once the chief probably of all the Roman clans, was settled in this very quarter; the Janiculum formed a part of the city itself, and Ostia was a burgess colony or, in other words, a suburb.
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Reference address : https://www.ellopos.net/elpenor/rome/1-04-beginnings-rome.asp?pg=6