The far-scheming king laid the foundation of his new colonial power especially in the sea to the east of Italy, the more northern waters of which now became, for the first time, subject to a Greek maritime power.

About the year 367, Dionysius occupied and colonized the port of Lissus and island of Issa on the Illyrian coast, and the ports of Ancona, Numana, and Atria, on the coast of Italy.

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) 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.