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
The Celts dwelt only in the intermediate flat country, the Insubres and Cenomani to the north of the Po, the Boii to the south, and--not to mention smaller tribes --the Senones on the coast of the Adriatic, from Ariminum to Ancona, in the so-called "country of the Gauls" (-ager Gallicus-). But even there Etruscan settlements must have continued partially at least to subsist, somewhat as Ephesus and Miletus remained Greek under the supremacy of the Persians.
Mantua at any rate, which was protected by its insular position, was a Tuscan city even in the time of the empire, and Atria on the Po also, where numerous discoveries of vases have been made, appears to have retained its Etruscan character; the description of the coasts that goes under the name of Scylax, composed about 418, calls the district of Atria and Spina Tuscan land.
This alone, moreover, explains how Etruscan corsairs could render the Adriatic unsafe till far into the fifth century, and why not only Dionysius of Syracuse covered its coasts with colonies, but even Athens, as a remarkable document recently discovered informs us, resolved about 429 to establish a colony in the Adriatic for the protection of seafarers against the Tyrrhene pirates.
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Reference address : https://www.ellopos.net/elpenor/rome/2-04-fall-etruscan-celts.asp?pg=30