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
Battle of Telamon
All this, however, required time. For once the Romans had allowed themselves to be surprised, and it was too late at least to save Etruria. The Celts found the Apennines hardly defended, and plundered unopposed the rich plains of the Tuscan territory, which for long had seen no enemy. They were already at Clusium, three days' march from Rome, when the army of Ariminum, under the consul Papus, appeared on their flank, while the Etruscan militia, which after crossing the Apennines had assembled in rear of the Gauls, followed the line of the enemy's march.
Suddenly one evening, after the two armies had already encamped and the bivouac fires were kindled, the Celtic infantry again broke up and retreated on the road towards Faesulae (Fiesole): the cavalry occupied the advanced posts during the night, and followed the main force next morning. When the Tuscan militia, who had pitched their camp close upon the enemy, became aware of his departure, they imagined that the host had begun to disperse, and marched hastily in pursuit.
The Gauls had reckoned on this very result: their infantry, which had rested and was drawn up in order, awaited on a well-chosen battlefield the Roman militia, which came up from its forced march fatigued and disordered. Six thousand men fell after a furious combat, and the rest of the militia, which had been compelled to seek refuge on a hill, would have perished, had not the consular army appeared just in time.
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Reference address : https://www.ellopos.net/elpenor/rome/3-03-extension-italy.asp?pg=33