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 these victories had an effect which the victors did not anticipate. For a considerable period an "unsettled people" had been wandering along the northern verge of the country occupied by the Celts on both sides of the Danube. They called themselves the Cimbri, that is, the Chempho, the champions or, as their enemies translated it, the robbers; a designation, however, which to all appearance had become the name of the people even before their migration.
They came from the north, and the first Celtic people with whom they came in contact were, so far as is known, the Boii, probably in Bohemia. More exact details as to the cause and the direction of their migration have not been recorded by contemporaries,(17) and cannot be supplied by conjecture, since the state of things in those times to the north of Bohemia and the Main and to the east of the Lower Rhine lies wholly beyond our knowledge.
17. The account that large tracts on the coasts of the North Sea had been torn away by inundations, and that this had occasioned the migration of the Cimbri in a body (Strabo, vii. 293), does not indeed appear to us fabulous, as it seemed to those who recorded it; but whether it was based on tradition or on conjecture, cannot be decided.
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Reference address : https://www.ellopos.net/elpenor/rome/4-05-peoples-north.asp?pg=24