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, however, by negotiations with the Helvetii, who would gladly have effected by peaceable means the crossing of the river and the march through the Allobrogian territory, gained a respite of fifteen days, which was employed in breaking down the bridge over the Rhone at Genava, and barring the southern bank of the Rhone against the enemy by an entrenchment nearly nineteen miles long: it was the first application of the system--afterwards carried out on so immense a scale by the Romans--of guarding the frontier of the empire in a military point of view by a chain of forts placed in connection with each other by ramparts and ditches.
The attempts of the Helvetii to gain the other bank at different places in boats or by means of fords were successfully frustrated by the Romans in these lines, and the Helvetii were compelled to desist from the passage of the Rhone.
Do you see any typos or other mistakes? Please let us know and correct them
Reference address : https://www.ellopos.net/elpenor/rome/5-07-subjugation-west.asp?pg=60