History of the Peloponnesian War

Exercising then what was at first a leadership over allies who were autonomous and took part in tle deliberations of common assemblies, the Athenians, in the interval between this war and the Persian, undertook, both in war and in the administration of public affairs, the enterprises now to be related, which were directed against the Barbarian, against their own allies when they attempted revolution, and against such of the Peloponnesians as from time to time came into conflict with them in the course of each attempt.

And I have made a digression to write of these matters for the reason that this period has been omitted by all my predecessors, wlo have confined their narratives either to Hellenic affairs before the Persian War or to the Persian War itself; and Hellanicus, the only one of these who has ever touched upon this period, has in his Attic History treated of it briefly, and with inaccuracy as regards his chronology. And at the same time the narrative of these events serves to explain how the empire of Athens was established.