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 Tiber and Its Traffic
This cannot have been the result of mere accident. The Tiber was the natural highway for the traffic of Latium; and its mouth, on a coast scantily provided with harbours, became necessarily the anchorage of seafarers. Moreover, the Tiber formed from very ancient times the frontier defence of the Latin stock against their northern neighbours. There was no place better fitted for an emporium of the Latin river and sea traffic, and for a maritime frontier fortress of Latium, than Rome. It combined the advantages of a strong position and of immediate vicinity to the river; it commanded both banks of the stream down to its mouth; it was so situated as to be equally convenient for the river navigator descending the Tiber or the Anio, and for the seafarer with vessels of so moderate a size as those which were then used; and it afforded greater protection from pirates than places situated immediately on the coast.
That Rome was indebted, if not for its origin, at any rate for its importance, to these commercial and strategical advantages of its position, there are accordingly numerous further indications, which are of very different weight from the statements of quasi-historical romances. Thence arose its very ancient relations with Caere, which was to Etruria what Rome was to Latium, and accordingly became Rome's most intimate neighbour and commercial ally. Thence arose the unusual importance of the bridge over the Tiber, and of bridge-building generally in the Roman commonwealth. Thence came the galley in the city arms; thence, too, the very ancient Roman port-duties on the exports and imports of Ostia, which were from the first levied only on what was to be exposed for sale (-promercale-), not on what was for the shipper's own use (-usuarium-), and which were therefore in reality a tax upon commerce.
Thence, to anticipate, the comparatively early occurrence in Rome of coined money, and of commercial treaties with transmarine states. In this sense, then, certainly Rome may have been, as the legend assumes, a creation rather than a growth, and the youngest rather than the oldest among the Latin cities. Beyond doubt the country was already in some degree cultivated, and the Alban range as well as various other heights of the Campagna were occupied by strongholds, when the Latin frontier emporium arose on the Tiber. Whether it was a resolution of the Latin confederacy, or the clear-sighted genius of some unknown founder, or the natural development of traffic, that called the city of Rome into being, it is vain even to surmise.
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Reference address : https://www.ellopos.net/elpenor/rome/1-04-beginnings-rome.asp?pg=7