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 Celtic, Galatian, or Gallic nation received from the common mother endowments different from those of its Italian, Germanic, and Greek sisters. With various solid qualities and still more that were brilliant, it was deficient in those deeper moral and political qualifications which lie at the root of all that is good and great in human development. It was reckoned disgraceful, Cicero tells us, for the free Celts to till their fields with their own hands. They preferred a pastoral life to agriculture; and even in the fertile plains of the Po they chiefly practised the rearing of swine, feeding on the flesh of their herds, and staying with them in the oak forests day and night.
Attachment to their native soil, such as characterized the Italians and the Germans, was wanting in the Celts; while on the other hand they delighted to congregate in towns and villages, which accordingly acquired magnitude and importance among the Celts earlier apparently than in Italy. Their political constitution was imperfect. Not only was the national unity recognized but feebly as a bond of connection--as is, in fact, the case with all nations at first--but the individual communities were deficient in concord and firm control, in earnest public spirit and consistency of aim.
The only organization for which they were fitted was a military one, where the bonds of discipline relieved the individual from the troublesome task of self-control. "The prominent qualities of the Celtic race," says their historian Thierry, "were personal bravery, in which they excelled all nations; an open impetuous temperament, accessible to every impression; much intelligence, but at the same time extreme mobility, want of perseverance, aversion to discipline and order, ostentation and perpetual discord--the result of boundless vanity."
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Reference address : https://www.ellopos.net/elpenor/rome/2-04-fall-etruscan-celts.asp?pg=10