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
With a view to cover the frontier of the Rhine and the immediately
threatened territory of the Allobroges, a Roman army under Marcus
Junius Silanus appeared in 645 in Southern Gaul. The Cimbri
requested that land might be assigned to them where they might
peacefully settle--a request which certainly could not be granted.
The consul instead of replying attacked them; he was utterly defeated
and the Roman camp was taken. The new levies which were occasioned
by this misfortune were already attended with so much difficulty, that
the senate procured the abolition of the laws--presumably proceeding
from Gaius Gracchus--which limited the obligation to military service
in point of time.(19)
But the Cimbri, instead of following up their
victory over the Romans, sent to the senate at Rome to repeat their
request for the assignment of land, and meanwhile employed themselves,
apparently, in the subjugation of the surrounding Celtic cantons.