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
The Catastrophe of the Celtic Nation - Traits Common to the Celts and Irish
All was over with the Celtic nation. Its political dissolution had been completed by Caesar; its national dissolution was begun and in course of regular progress. This was no accidental destruction, such as destiny sometimes prepares even for peoples capable of development, but a self-incurred and in some measure historically necessary catastrophe. The very course of the last war proves this, whether we view it as a whole or in detail. When the establishment of the foreign rule was in contemplation, only single districts-- mostly, moreover, German or half-German--offered energetic resistance.
When the foreign rule was actually established, the attempts to shake it off were either undertaken altogether without judgment, or they were to an undue extent the work of certain prominent nobles, and were therefore immediately and entirely brought to an end with the death or capture of an Indutiomarus, Camulogenus, Vercingetorix, or Correus. The sieges and guerilla warfare, in which elsewhere the whole moral depth of national struggles displays itself, were throughout this Celtic struggle of a peculiarly pitiable character. Every page of Celtic history confirms the severe saying of one of the few Romans who had the judgment not to despise the so-called barbarians--that the Celts boldly challenge danger while future, but lose their courage before its presence.
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Reference address : https://www.ellopos.net/elpenor/rome/5-07-subjugation-west.asp?pg=139