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
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.
