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
Development of Knighthood - Breaking Up of the Old Cantonal Constitution
It is simply the reverse side of the total want of urban
commonwealths among the Celts just noticed, that the opposite pole
of political development, knighthood, so thoroughly preponderates
in the Celtic clan-constitution.
The Celtic aristocracy was to all
appearance a high nobility, for the most part perhaps the members
of the royal or formerly royal families; as indeed it is remarkable
that the heads of the opposite parties in the same clan
very frequently belong to the same house. These great families
combined in their hands financial, warlike, and political ascendency.
They monopolized the leases of the profitable rights of the state.
They compelled the free commons, who were oppressed by the burden
of taxation, to borrow from them, and to surrender their freedom
first de facto as debtors, then de jure as bondmen.