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
Outbreak of War between Samnium and Rome-- Pacification of Campania
Differences had already for several years existed between Rome and Samnium in consequence of the continual aggressions in which the Romans indulged on the Liris, and of which the founding of Fregellae in 426 was the latest and most important. But it was the Greeks of Campania that gave occasion to the outbreak of the contest.
After Cumae and Capua had become Roman, nothing so naturally suggested itself to the Romans as the subjugation of the Greek city Neapolis, which ruled also over the Greek islands in the bay--the only town not yet reduced to subjection within the field of the Roman power.
The Tarentines and Samnites, informed of the scheme of the Romans to obtain possession of the town, resolved to anticipate them; and while the Tarentines were too remiss perhaps rather than too distant for the execution of this plan, the Samnites actually threw into it a strong garrison. The Romans immediately declared war nominally against the Neapolitans, really against the Samnites (427), and began the siege of Neapolis.
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Reference address : https://www.ellopos.net/elpenor/rome/2-06-italians-rome.asp?pg=6