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
Natural Boundaries of Italy
The Italian confederacy as it emerged from the crises of the fifth century--or, in other words, the State of Italy--united the various civic and cantonal communities from the Apennines to the Ionian Sea under the hegemony of Rome. But before the close of the fifth century these limits were already overpassed in both directions, and Italian communities belonging to the confederacy had sprung up beyond the Apennines and beyond the sea. In the north the republic, in revenge for ancient and recent wrongs, had already in 471 annihilated the Celtic Senones; in the south, through the great war from 490 to 513, it had dislodged the Phoenicians from the island of Sicily.
In the north there belonged to the combination headed by Rome the Latin town of Ariminum (besides the burgess-settlement of Sena), in the south the community of the Mamertines in Messana, and as both were nationally of Italian origin, so both shared in the common rights and obligations of the Italian confederacy. It was probably the pressure of events at the moment rather than any comprehensive political calculation, that gave rise to these extensions of the confederacy; but it was natural that now at least, after the great successes achieved against Carthage, new and wider views of policy should dawn upon the Roman government--views which even otherwise were obviously enough suggested by the physical features of the peninsula.
Alike in a political and in a military point of view Rome was justified in shifting its northern boundary from the low and easily crossed Apennines to the mighty mountain-wall that separates northern from southern Europe, the Alps, and in combining with the sovereignty of Italy the sovereignty of the seas and islands on the west and east of the peninsula; and now, when by the expulsion of the Phoenicians from Sicily the most difficult portion of the task had been already achieved, various circumstances united to facilitate its completion by the Roman government.
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Reference address : https://www.ellopos.net/elpenor/rome/3-03-extension-italy.asp