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 lack of information, however, is not much felt; for this race, already on the decline at the period when our history begins, comes before us only when it is giving way and disappearing. The character of the Iapygian people, little capable of resistance, easily merging into other nationalities, agrees well with the hypothesis, to which their geographical position adds probability, that they were the oldest immigrants or the historical autochthones of Italy. There can be no doubt that all the primitive migrations of nations took place by land; especially such as were directed towards Italy, the coast of which was accessible by sea only to skilful sailors and on that account was still in Homer's time wholly unknown to the Greeks. But if the earlier settlers came over the Apennines, then, as the geologist infers the origin of mountains from their stratification, the historical inquirer may hazard the conjecture that the stocks pushed furthest towards the south were the oldest inhabitants of Italy; and it is just at its extreme south-eastern verge that we meet with the Iapygian nation.
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Reference address : https://www.ellopos.net/elpenor/rome/1-02-earliest-migrations-italy.asp?pg=5