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 complete credibility of these accounts must certainly remain doubtful, since, as Tacitus remarks in reference to the two peoples last mentioned, it was subsequently, at least in these regions, reckoned an honour to be descended of German blood and not to belong to the little-esteemed Celtic nation; yet the population in the region of the Scheldt, Maas, and Moselle seems certainly to have become, in one way or another, largely mingled with German elements, or at any rate to have come under German influences. The German settlements themselves were perhaps small; they were not unimportant, for amidst the chaotic obscurity, through which we see the stream of peoples on the right bank of the Rhine ebbing and flowing about this period, we can well perceive that larger German hordes were preparing to cross the Rhine in the track of these advanced posts.
Threatened on two sides by foreign domination and torn by internal dissension, it was scarcely to be expected that the unhappy Celtic nation would now rally and save itself by its own vigour. Dismemberment, and decay in virtue of dismemberment, had hitherto been its history; how should a nation, which could name no day like those of Marathon and Salamis, of Aricia and the Raudine plain--a nation which, even in its time of vigour, had made no attempt to destroy Massilia by a united effort--now when evening had come, defend itself against so formidable foes?
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Reference address : https://www.ellopos.net/elpenor/rome/5-07-subjugation-west.asp?pg=49