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
But even the united hordes were unable to overcome the brave resistance of the Belgae. The leaders accordingly resolved, now that their numbers were thus swelled, to enter in all earnest on the expedition to Italy which they had several times contemplated. In order not to encumber themselves with the spoil which they had heretofore collected, they left it behind under the protection of a division of 6000 men, which after many wanderings subsequently gave rise to the tribe of the Aduatuci on the Sambre.
But, whether from the difficulty of finding supplies on the Alpine routes or from other reasons, the mass again broke up into two hosts, one of which, composed of the Cimbri and Tigorini, was to recross the Rhine and to invade Italy through the passes of the eastern Alps already reconnoitred in 641, and the other, composed of the newly-arrived Teutones, the Tougeni, and the Ambrones--the flower of the Cimbrian host already tried in the battle of Arausio--was to invade Italy through Roman Gaul and the western passes.
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Reference address : https://www.ellopos.net/elpenor/rome/4-05-peoples-north.asp?pg=44