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
Fresh Violations of the Rhine-Boundary by the Germans - The Usipetes and Tencteri
One of the objects which Caesar had proposed to himself--
the subjugation of Gaul--had been in substance, with exceptions
scarcely worth mentioning, attained so far as it could be attained
at all by the sword. But the other half of the work undertaken
by Caesar was still far from being satisfactorily accomplished,
and the Germans had by no means as yet been everywhere compelled
to recognize the Rhine as their limit. Even now, in the winter
of 698-699, a fresh crossing of the boundary had taken place
on the lower course of the river, whither the Romans had not yet
penetrated. The German tribes of the Usipetes and Tencteri
whose attempts to cross the Rhine in the territory of the Menapii
have been already mentioned,(41) had at length, eluding the vigilance
of their opponents by a feigned retreat, crossed in the vessels
belonging to the Menapii--an enormous host, which is said,
including women and children, to have amounted to 430,000 persons.