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
Lastly, the territory of the most easterly clan of the Celts, the warlike and numerous Helvetii, was visited with growing frequency by the Germans, so that the Helvetii, who perhaps even apart from this were suffering from over-population through the reflux of their settlers from the territory which they had lost to the north of the Rhine, and besides were liable to be completely isolated from their kinsmen by the settlement of Ariovistus in the territory of the Sequani, conceived the desperate resolution of voluntarily evacuating the territory hitherto in their possession to the Germans, and acquiring larger and more fertile abodes to the west of the Jura, along with, if possible, the hegemony in the interior of Gaul--a plan which some of their districts had already formed and attempted to execute during the Cimbrian invasion.(32)
32. Cf. IV. V. Inroad of the Helvetii into Southern Gaul
The Rauraci whose territory (Basle and southern Alsace) was similarly threatened, the remains, moreover, of the Boii who had already at an earlier period been compelled by the Germans to forsake their homes and were now unsettled wanderers, and other smaller tribes, made common cause with the Helvetii. As early as 693 their flying parties came over the Jura and even as far as the Roman province; their departure itself could not be much longer delayed; inevitably German settlers would then advance into the important region between the lakes of Constance and Geneva forsaken by its defenders. From the sources of the Rhine to the Atlantic Ocean the German tribes were in motion; the whole line of the Rhine was threatened by them; it was a moment like that when the Alamanni and the Franks threw themselves on the falling empire of the Caesars; and even now there seemed on the eve of being carried into effect against the Celts that very movement which was successful five hundred years afterwards against the Romans.
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Reference address : https://www.ellopos.net/elpenor/rome/5-07-subjugation-west.asp?pg=56