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
If we survey the whole condition of the Celts as Caesar found it
in the Transalpine regions, there is an unmistakeable advance
in civilization, as compared with the stage of culture at which
the Celts came before us a century and a half previously in the valley
of the Po. Then the militia, excellent of its kind, thoroughly
preponderated in their armies;(23) now the cavalry occupies
the first place.
Then the Celts dwelt in open villages; now well-
constructed walls surrounded their townships. The objects too
found in the tombs of Lombardy are, especially as respects articles
of copper and glass, far inferior to those of northern Gaul.
Perhaps the most trustworthy measure of the increase of culture
is the sense of a common relationship in the nation; so little
of it comes to light in the Celtic battles fought on the soil of what
is now Lombardy, while it strikingly appears in the struggles
against Caesar.