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 memory of the Syracusan dominion in this remote region is preserved not only by the "trenches of Philistus," a canal constructed at the mouth of the Po beyond doubt by the well-known historian and friend of Dionysius who spent the years of his exile (368 et seq.) at Atria, but also by the alteration in the name of the Italian eastern sea itself, which from this time forth, instead of its earlier designation of the "Ionic Gulf",(3) received the appellation still current at the present day, and probably referable to these events, of the sea "of Hadria."(4)
3. Cf. I. X. Home of the Greek Immigrants
4. Hecataeus (after 257 u. c.) and Herodotus also (270-after 345) only know Hatrias as the delta of the Po and the sea that washes its shores (O. Muller, Etrusker, i. p. 140; Geogr. Graeci min. ed. C. Muller, i. p. 23). The appellation of Adriatic sea, in its more extended sense, first occurs in the so-called Scylax about 418 U. C.
But not content with these attacks on the possessions and commercial communications of the Etruscans in the eastern sea, Dionysius assailed the very heart of the Etruscan power by storming and plundering Pyrgi, the rich seaport of Caere (369). From this blow it never recovered. When the internal disturbances that followed the death of Dionysius in Syracuse gave the Carthaginians freer scope, and their fleet resumed in the Tyrrhene sea that ascendency which with but slight interruptions they thenceforth maintained, it proved a burden no less grievous to Etruscans than to Greeks; so that, when Agathocles of Syracuse in 444 was making preparations for war with Carthage, he was even joined by eighteen Tuscan vessels of war. The Etruscans perhaps had their fears in regard to Corsica, which they probably still at that time retained. The old Etrusco-Phoenician symmachy, which still existed in the time of Aristotle (370-432), was thus broken up; but the Etruscans never recovered their maritime strength.
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Reference address : https://www.ellopos.net/elpenor/rome/2-04-fall-etruscan-celts.asp?pg=7