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
Caesar sent Labienus with all the cavalry to the Rhine, with a view to hold in check the agitation in the Belgic province, and in case of need to prevent the Germans from crossing the river; another of his lieutenants, Quintus Titurius Sabinus, went with three legions to Normandy, where the main body of the insurgents assembled. But the powerful and intelligent Veneti were the true centre of the insurrection; the chief attack by land and sea was directed against them. Caesar's lieutenant, Decimus Brutus, brought up the fleet formed partly of the ships of the subject Celtic cantons, partly of a number of Roman galleys hastily built on the Loire and manned with rowers from the Narbonese province; Caesar himself advanced with the flower of his infantry into the territory of the Veneti.
But these were prepared beforehand, and had with equal skill and resolution availed themselves of the favourable circumstances which the nature of the ground in Brittany and the possession of a considerable naval power presented. The country was much intersected and poorly furnished with grain, the towns were situated for the most part on cliffs and tongues of land, and were accessible from the mainland only by shallows which it was difficult to cross; the provision of supplies and the conducting of sieges were equally difficult for the army attacking by land, while the Celts by means of their vessels could furnish the towns easily with everything needful, and in the event of the worst could accomplish their evacuation. The legions expended their time and strength in the sieges of the Venetian townships, only to see the substantial fruits of victory ultimately carried off in the vessels of the enemy.
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Reference address : https://www.ellopos.net/elpenor/rome/5-07-subjugation-west.asp?pg=81