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
Relations between the Palatine and Quirinal Communities
Thus the site of the Roman commonwealth was still at this period occupied by the Mount-Romans of the Palatine and the Hill-Romans of the Quirinal as two separate communities confronting each other and doubtless in many respects at feud, in some degree resembling the Montigiani and the Trasteverini in modern Rome. That the community of the Seven Mounts early attained a great preponderance over that of the Quirinal may with certainty be inferred both from the greater extent of its newer portions and suburbs, and from the position of inferiority in which the former Hill-Romans were obliged to acquiesce under the later Servian arrangement. But even within the Palatine city there was hardly a true and complete amalgamation of the different constituent elements of the settlement.
We have already mentioned how the Subura and the Palatine annually contended for the horse's head; the several Mounts also, and even the several curies (there was as yet no common hearth for the city, but the various hearths of the curies subsisted side by side, although in the same locality) probably felt themselves to be as yet more separated than united; and Rome as a whole was probably rather an aggregate of urban settlements than a single city. It appears from many indications that the houses of the old and powerful families were constructed somewhat after the manner of fortresses and were rendered capable of defence--a precaution, it may be presumed, not unnecessary. It was the magnificent structure ascribed to king Servius Tullius that first surrounded not merely those two cities of the Palatine and Quirinal, but also the heights of the Capitol and the Aventine which were not comprehended within their enclosure, with a single great ring-wall, and thereby created the new Rome--the Rome of history. But ere this mighty work was undertaken, the relations of Rome to the surrounding country had beyond doubt undergone a complete revolution.
As the period, during which the husbandman guided his plough on the seven hills of Rome just as on the other hills of Latium, and the usually unoccupied places of refuge on particular summits alone presented the germs of a more permanent settlement, corresponds to the earliest epoch of the Latin stock without trace of traffic or achievement; as thereafter the flourishing settlement on the Palatine and in the "Seven Rings" was coincident with the occupation of the mouths of the Tiber by the Roman community, and with the progress of the Latins to a more stirring and freer intercourse, to an urban civilization in Rome more especially, and perhaps also to a more consolidated political union in the individual states as well as in the confederacy; so the Servian wall, which was the foundation of a single great city, was connected with the epoch at which the city of Rome was able to contend for, and at length to achieve, the sovereignty of the Latin league.
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Reference address : https://www.ellopos.net/elpenor/rome/1-04-beginnings-rome.asp?pg=17