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
Each of these leagues consisted of twelve communities, which recognized a metropolis, especially for purposes of worship, and a federal head or rather a high priest, but appear to have been substantially equal in respect of rights; while some of them at least were so powerful that neither could a hegemony establish itself, nor could the central authority attain consolidation.
In Etruria proper Volsinii was the metropolis; of the rest of its twelve towns we know by trustworthy tradition only Perusia, Vetulonium, Volci, and Tarquinii. It was, however, quite as unusual for the Etruscans really to act in concert, as it was for the Latin confederacy to do otherwise. Wars were ordinarily carried on by a single community, which endeavoured to interest in its cause such of its neighbours as it could; and when an exceptional case occurred in which war was resolved on by the league, individual towns very frequently kept aloof from it.
The Etruscan confederations appear to have been from the first--still more than the other Italian leagues formed on a similar basis of national affinity--deficient in a firm and paramount central authority.
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Reference address : https://www.ellopos.net/elpenor/rome/1-09-etruscans.asp?pg=15