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
On the other hand the Gauls doubtless employed in the Channel in Caesar's time, as for long afterwards, a species of portable leathern skiffs, which seem to have been in the main common oared boats, but on the west coast of Gaul the Santones, the Pictones, and above all the Veneti sailed in large though clumsily built ships, which were not impelled by oars but were provided with leathern sails and iron anchor-chains; and they employed these not only for their traffic with Britain, but also in naval combat.
Here therefore we not only meet for the first time with navigation in the open ocean, but we find that here the sailing vessel first fully took the place of the oared boat--an improvement, it is true, which the declining activity of the old world did not know how to turn to account, and the immeasurable results of which our own epoch of renewed culture is employed in gradually reaping.
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Reference address : https://www.ellopos.net/elpenor/rome/5-07-subjugation-west.asp?pg=21