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
Earliest Boundaries of the Italian Confederacy
The earliest boundaries of this great armed confederacy led by Rome, or of the new Italy, reached on the western coast as far as the district of Leghorn south of the Arnus,(44) on the east as far as the Aesis north of Ancona.
44. This earliest boundary is probably indicated by the two small townships -Ad fines-, of which one lay north of Arezzo on the road to Florence, the second on the coast not far from Leghorn. Somewhat further to the south of the latter, the brook and valley of Vada are still called -Fiume della fine-, -Valle della fine- (Targioni Tozzetti, Viaggj, iv. 430).
The townships colonized by Italians, lying beyond these limits, such as Sena Gallica and Ariminum beyond the Apennines, and Messana in Sicily, were reckoned geographically as situated out of Italy--even when, like Ariminum, they were members of the confederacy or even, like Sena, were Roman burgess communities. Still less could the Celtic cantons beyond the Apennines be reckoned among the -togati-, although perhaps some of them were already among the clients of Rome.
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Reference address : https://www.ellopos.net/elpenor/rome/2-07-pyrrhus-rome-italy.asp?pg=85