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 middle of the peninsula was inhabited, as far back as trustworthy tradition reaches, by two peoples or rather two branches of the same people, whose position in the Indo-Germanic family admits of being determined with greater precision than that of the Iapygian nation. We may with propriety call this people the Italian, since upon it rests the historical significance of the peninsula. It is divided into the two branch-stocks of the Latins and the Umbrians; the latter including their southern offshoots, the Marsians and Samnites, and the colonies sent forth by the Samnites in historical times. The philological analysis of the idioms of these stocks has shown that they together constitute a link in the Indo-Germanic chain of languages, and that the epoch in which they still formed an unity is a comparatively late one. In their system of sounds there appears the peculiar spirant -f, in the use of which they agree with the Etruscans, but decidedly differ from all Greek and Graeco-barbaric races as well as from the Sanscrit itself.
The aspirates, again, which are retained by the Greeks throughout, and the harsher of them also by the Etruscans, were originally foreign to the Italians, and are represented among them by one of their elements--either by the media, or by the breathing alone -f or -h. The finer spirants, -s, -w, -j, which the Greeks dispense with as much as possible, have been retained in the Italian languages almost unimpaired, and have been in some instances still further developed. The throwing back of the accent and the consequent destruction of terminations are common to the Italians with some Greek stocks and with the Etruscans; but among the Italians this was done to a greater extent than among the former, and to a lesser extent than among the latter. The excessive disorder of the terminations in the Umbrian certainly had no foundation in the original spirit of the language, but was a corruption of later date, which appeared in a similar although weaker tendency also at Rome.
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Reference address : https://www.ellopos.net/elpenor/rome/1-02-earliest-migrations-italy.asp?pg=6