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
The Germans on the Lower Rhine - The Germans on the Upper Rhine - Spread of the Helvetian Invasion to the Interior of Gaul
The appearance of the energetic German prince in so dangerous
proximity, which could not but in itself excite the most serious
apprehension in the Romans, appeared still more threatening,
inasmuch as it stood by no means alone. The Usipetes and Tencteri
settled on the right bank of the Rhine, weary of the incessant
devastation of their territory by the overbearing Suebian tribes,
had, the year before Caesar arrived in Gaul (695), set out
from their previous abodes to seek others at the mouth of the Rhine.
They had already taken away from the Menapii there the portion
of their territory situated on the right bank, and it might be
foreseen that they would make the attempt to establish themselves
also on the left. Suebian bands, moreover, assembled between
Cologne and Mayence, and threatened to appear as uninvited guests
in the opposite Celtic canton of the Treveri.