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 Lucanians and Bruttians, thus cheated by their more powerful allies of their share in the common spoil, entered into negotiations with the opposition-party among the Samnites and Tarentines to bring about a new Italian coalition; and when the Romans sent an embassy to warn them, they detained the envoys in captivity and began the war against Rome with a new attack on Thurii (about 469), while at the same time they invited not only the Samnites and Tarentines, but the northern Italians also--the Etruscans, Umbrians, and Gauls--to join them in the struggle for freedom.
The Etruscan league actually revolted, and hired numerous bands of Gauls; the Roman army, which the praetor Lucius Caecilius was leading to the help of the Arretines who had remained faithful, was annihilated under the walls of Arretium by the Senonian mercenaries of the Etruscans: the general himself fell with 13,000 of his men (470). The Senones were reckoned allies of Rome; the Romans accordingly sent envoys to them to complain of their furnishing warriors to serve against Rome, and to require the surrender of their captives without ransom. But by the command of their chieftain Britomaris, who had to take vengeance on the Romans for the death of his father, the Senones slew the Roman envoys and openly took the Etruscan side.
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Reference address : https://www.ellopos.net/elpenor/rome/2-07-pyrrhus-rome-italy.asp?pg=12