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
Naval Battle between the Romans and the Veneti - Submission of the Maritime Cantons
Accordingly when the Roman fleet, long detained by storms at the mouth of the Loire, arrived at length on the coast of Brittany, it was left to decide the struggle by a naval battle. The Celts, conscious of their superiority on this element, brought forth their fleet against that of the Romans commanded by Brutus. Not only did it number 220 sail, far more than the Romans had been able to bring up, but their high-decked strong sailing-vessels with flat bottoms were also far better adapted for the high-running waves of the Atlantic Ocean than the low, lightly-built oared galleys of the Romans with their sharp keels.
Neither the missiles nor the boarding-bridges of the Romans could reach the high deck of the enemy's vessels, and the iron beaks recoiled powerless from the strong oaken planks. But the Roman mariners cut the ropes, by which the yards were fastened to the masts, by means of sickles fastened to long poles; the yards and sails fell down, and, as they did not know how to repair the damage speedily, the ship was thus rendered a wreck just as it is at the present day by the falling of the masts, and the Roman boats easily succeeded by a joint attack in mastering the maimed vessel of the enemy.
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Reference address : https://www.ellopos.net/elpenor/rome/5-07-subjugation-west.asp?pg=82