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
From: The History of Rome, by Theodor Mommsen
Translated with the sanction of the author by William Purdie Dickson
Want of Political Centralization - The Canton-Leagues
But while the sense of mutual relationship was thus vividly awakened among the Celtic tribes, the nation was still precluded from attaining a basis of political centralization such as Italy found in the Roman burgesses, and the Greeks and Germans in the Macedonian and Frank kings. The Celtic priesthood and likewise the nobility--although both in a certain sense represented and combined the nation--were yet, on the one hand, incapable of uniting it in consequence of their particular class-interests, and, on the other hand, sufficiently powerful to allow no king and no canton to accomplish the work of union.
Attempts at this work were not wanting; they followed, as the cantonal constitution suggested, the system of hegemony. A powerful canton induced a weaker to become subordinate, on such a footing that the leading canton acted for the other as well as for itself in its external relations and stipulated for it in state-treaties, while the dependent canton bound itself to render military service and sometimes also to pay a tribute. In this way a series of separate leagues arose; but there was no leading canton for all Gaul--no tie, however loose, combining the nation as a whole.
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Reference address : https://www.ellopos.net/elpenor/rome/5-07-subjugation-west.asp?pg=34