History of the Peloponnesian War

Now using their authority at first in such manner as that the confederates lived under their own laws and were admitted to common council, by [the] war and administration of the common affairs of Greece from the Persian war to this, what against the barbarians, what against their own innovating confederates, and what against such of the Peloponnesians as chanced always in every war to fall in, they effected those great matters following.

Which also I have therefore written both because this place hath been pretermitted by all that have written before me (for they have either compiled the Grecian acts before the invasion of the Persians or that invasion only, of which number is Hellanicus, who hath also touched them in his Attic history, but briefly and without exact mention of the times), and also because they carry with them a demonstration of how the Athenian empire grew up.