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
Pacification of Northern Italy
In northern Italy likewise the peoples that had come into collision and conflict gradually settled on a permanent footing and within more defined limits. The migrations over the Alps ceased, partly perhaps in consequence of the desperate defence which the Etruscans made in their more restricted home, and of the serious resistance of the powerful Romans, partly perhaps also in consequence of changes unknown to us on the north of the Alps.
Between the Alps and the Apennines, as far south as the Abruzzi, the Celts were now generally the ruling nation, and they were masters more especially of the plains and rich pastures; but from the lax and superficial nature of their settlement their dominion took no deep root in the newly acquired land and by no means assumed the shape of exclusive possession. How matters stood in the Alps, and to what extent Celtic settlers became mingled there with earlier Etruscan or other stocks, our unsatisfactory information as to the nationality of the later Alpine peoples does not permit us to ascertain; only the Raeti in the modern Grisons and Tyrol may be described as a probably Etruscan stock.
The Umbrians retained the valleys of the Apennines, and the Veneti, speaking a different language, kept possession of the north-eastern portion of the valley of the Po. Ligurian tribes maintained their footing in the western mountains, dwelling as far south as Pisa and Arezzo, and separating the Celt-land proper from Etruria.
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Reference address : https://www.ellopos.net/elpenor/rome/2-04-fall-etruscan-celts.asp?pg=29