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 contemporary attacks of the Celts would alone suffice to explain the nonintervention of the northern communities; it is affirmed however, and there is no reason to doubt, that this inaction of the other Etruscans was primarily occasioned by internal factions in the league of the Etruscan cities, and particularly by the opposition which the regal form of government retained or restored by the Veientes encountered from the aristocratic governments of the other cities.
Had the Etruscan nation been able or willing to take part in the conflict, the Roman community would hardly have been able --undeveloped as was the art of besieging at that time--to accomplish the gigantic task of subduing a large and strong city. But isolated and forsaken as Veii was, it succumbed (358) after a valiant resistance to the persevering and heroic spirit of Marcus Furius Camillus, who first opened up to his countrymen the brilliant and perilous career of foreign conquest.
The joy which this great success excited in Rome had its echo in the Roman custom, continued down to a late age, of concluding the festal games with a "sale of Veientes," at which, among the mock spoils submitted to auction, the most wretched old cripple who could be procured wound up the sport in a purple mantle and ornaments of gold as "king of the Veientes." The city was destroyed, and the soil was doomed to perpetual desolation.
Falerii and Capena hastened to make peace; the powerful Volsinii, which with federal indecision had remained quiet during the agony of Veii and took up arms after its capture, likewise after a few years (363) consented to peace. The statement that the two bulwarks of the Etruscan nation, Melpum and Veii, yielded on the same day, the former to the Celts, the latter to the Romans, may be merely a melancholy legend; but it at any rate involves a deep historical truth. The double assault from the north and from the south, and the fall of the two frontier strongholds, were the beginning of the end of the great Etruscan nation.
Do you see any typos or other mistakes? Please let us know and correct them
Reference address : https://www.ellopos.net/elpenor/rome/2-04-fall-etruscan-celts.asp?pg=19