History of the Peloponnesian War

Indeed, even after the Trojan war Hellas was still subject to migrations and in process of settlement, and hence did not get rest and wax stronger.

For not only did the return of the Hellenes from Ilium, occurring as it did after a long time, cause many changes; but factions also began to spring up very generally in the cities, and, in consequence of these, men were driven into exile and founded new cities.

The present Boeotians, for example, were driven from Arne by the Thessalians in the sixtieth year after the capture of Ilium and settled in the district now called Boeotia, but formerly CadmeYs; only a portion of these had been in that land before, and it was some of these who took part in the expedition against Ilium. The Dorians, too, in the eightieth year after the war, together with the Heracleidae occupied the Peloponnesus.

And so when painfully and after a long course of time Hellas became permanently tranquil and its population was no longer subject to expulsion from their homes, it began to send out colonies. The Athenians colonized lonia and most of the islands; the Peloponnesians, the greater part of Italy and Sicily and some portions of the rest of Hellas. And all these colonies were planted after the Trojan war.