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
Breach between Rome and Tarentum
The Tarentines since the treaty of 450 had lived at peace with Rome. They had been spectators of the long struggle of the Samnites, and of the rapid extirpation of the Senones; they had acquiesced without remonstrance in the establishment of Venusia, Atria, and Sena, and in the occupation of Thurii and of Rhegium. But when the Roman fleet, on its voyage from the Tyrrhene to the Adriatic sea, now arrived in the Tarentine waters and cast anchor in the harbour of the friendly city, the long, cherished resentment at length overflowed.
Old treaties, which prohibited the war-vessels of Rome from sailing to the east of the Lacinian promontory, were appealed to by popular orators in the assembly of the citizens. A furious mob fell upon the Roman ships of war, which, assailed suddenly in a piratical fashion, succumbed after a sharp struggle; five ships were taken and their crews executed or sold into slavery; the Roman admiral himself had fallen in the engagement. Only the supreme folly and supreme unscrupulousness of mob-rule can account for those disgraceful proceedings.
The treaties referred to belonged to a period long past and forgotten; it is clear that they no longer had any meaning, at least subsequently to the founding of Atria and Sena, and that the Romans entered the bay on the faith of the existing alliance; indeed, it was very much their interest--as the further course of things showed--to afford the Tarentines no sort of pretext for declaring war.
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Reference address : https://www.ellopos.net/elpenor/rome/2-07-pyrrhus-rome-italy.asp?pg=16