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
Celts and Germans
Still more violent even than the pressure of the Romans from the Mediterranean was that of the Germans downward from the Baltic and the North Sea--a fresh stock from the great cradle of peoples in the east, which made room for itself by the side of its elder brethren with youthful vigour, although also with youthful rudeness. Though the tribes of this stock dwelling nearest to the Rhine--the Usipetes, Tencteri, Sugambri, Ubii--had begun to be in some degree civilized, and had at least ceased voluntarily to change their abodes, all accounts yet agree that farther inland agriculture was of little importance, and the several tribes had hardly yet attained fixed abodes.
It is significant in this respect that their western neighbours at this time hardly knew how to name any one of the peoples of the interior of Germany by its cantonal name; these were only known to them under the general appellations of the Suebi, that is, the roving people or nomads, and the Marcomani, that is, the land-guard(25)--names which were hardly cantonal names in Caesar's time, although they appeared as such to the Romans and subsequently became in various cases names of cantons.
25. Caesar's Suebi thus were probably the Chatti; but that designation certainly belonged in Caesar's time, and even much later, also to every other German stock which could be described as a regularly wandering one. Accordingly if, as is not to be doubted, the "king of the Suebi" in Mela (iii. i) and Pliny (H. N. ii. 67, 170) was Ariovistus, it by no means therefore follows that Ariovistus was a Chattan. The Marcomani cannot be demonstrated as a distinct people before Marbod; it is very possible that the word up to that point indicates nothing but what it etymologically signifies--the land, or frontier, guard. When Caesar (i, 51) mentions Marcomani among the peoples fighting in the army of Ariovistus, he may in this instance have misunderstood a merely appellative designation, just as he has decidedly done in the case of the Suebi.
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Reference address : https://www.ellopos.net/elpenor/rome/5-07-subjugation-west.asp?pg=46