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 conventionally received tradition, which assumes the name of history, is composed of a few serviceable notices by civilized travellers, and a mass of mostly worthless legends, which have usually been combined with little discrimination of the true character either of legend or of history. But there is another source of tradition to which we may resort, and which yields information fragmentary but authentic; we mean the indigenous languages of the stocks settled in Italy from time immemorial. These languages, which have grown with the growth of the peoples themselves, have had the stamp of their process of growth impressed upon them too deeply to be wholly effaced by subsequent civilization. One only of the Italian languages is known to us completely; but the remains which have been preserved of several of the others are sufficient to afford a basis for historical inquiry regarding the existence, and the degrees, of family relationship among the several languages and peoples.
In this way philological research teaches us to distinguish three primitive Italian stocks, the Iapygian, the Etruscan, and that which we shall call the Italian. The last is divided into two main branches,--the Latin branch, and that to which the dialects of the Umbri, Marsi, Volsci, and Samnites belong.
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Reference address : https://www.ellopos.net/elpenor/rome/1-02-earliest-migrations-italy.asp?pg=3