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 next neighbours and kinsmen of the Senones, the Boii, terrified and exasperated by a catastrophe which had been accomplished with so fearful a rapidity, united instantaneously with the Etruscans, who still continued the war, and whose Senonian mercenaries now fought against the Romans no longer as hirelings, but as desperate avengers of their native land.
A powerful Etrusco-Gallic army marched against Rome to retaliate the annihilation of the Senonian tribe on the enemy's capital, and to extirpate Rome from the face of the earth more completely than had been formerly done by the chieftain of these same Senones. But the combined army was decidedly defeated by the Romans at its passage of the Tiber in the neighbourhood of the Vadimonian lake (471). After they had once more in the following year risked a general engagement near Populonia with no better success, the Boii deserted their confederates and concluded a peace on their own account with the Romans (472).
Thus the Gauls, the most formidable member of the league, were conquered in detail before the league was fully formed, and by that means the hands of Rome were left free to act against Lower Italy, where during the years 469-471 the contest had not been carried on with any vigour.
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Reference address : http://www.ellopos.net/elpenor/rome/2-07-pyrrhus-rome-italy.asp?pg=14