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
Foundation of a German Empire in Gaul
The German warrior-prince naturally took this as a renunciation by the Romans of the Celtic land which they had not occupied; he accordingly took up his abode there, and began to establish a German principality on Gallic soil. It was his intention that the numerous bands which he had brought with him, and the still more numerous bands that afterwards followed at his call from home-- it was reckoned that up to 696 some 120,000 Germans had crossed the Rhine--this whole mighty immigration of the German nation, which poured through the once opened sluices like a stream over the beautiful west, should become settled there and form a basis on which he might build his dominion over Gaul.
The extent of the German settlements which he called into existence on the left bank of the Rhine cannot be determined; beyond doubt it was great, and his projects were far greater still. The Celts were treated by him as a wholly subjugated nation, and no distinction was made between the several cantons. Even the Sequani, as whose hired commander-in-chief he had crossed the Rhine, were obliged, as if they were vanquished enemies, to cede to him for his people a third of their territory--presumably upper Alsace afterwards inhabited by the Triboci--where Ariovistus permanently settled with his followers; nay, as if this were not enough, a second third was afterwards demanded of them for the Harudes who arrived subsequently. Ariovistus seemed as if he wished to take up in Gaul the part of Philip of Macedonia, and to play the master over the Celts who were friendly to the Germans no less than over those who adhered to the Romans.
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Reference address : https://www.ellopos.net/elpenor/rome/5-07-subjugation-west.asp?pg=54