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 gates of the Alps, the mighty stream navigable for 230 miles, and the largest and most fertile plain of the then civilized Europe, still continued in the hands of the hereditary foes of the Italian name, who, humbled indeed and weakened, but still scarce even nominally dependent and still troublesome neighbours, persevered in their barbarism, and, thinly scattered over the spacious plains, continued to pasture their herds and to plunder.
It was to be anticipated that the Romans would hasten to possess themselves of these regions; the more so as the Celts gradually began to forget their defeats in the campaigns of 471 and 472 and to bestir themselves again, and, what was still more dangerous, the Transalpine Celts began anew to show themselves on the south of the Alps.
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Reference address : https://www.ellopos.net/elpenor/rome/3-03-extension-italy.asp?pg=28