History of the Peloponnesian War

It is thus that empire has been won, both by us and by all others that have held it, by a constant readiness to support all, whether barbarians or Hellenes, that invite assistance; since if all were to keep quiet or to pick and choose whom they ought to assist, we should make but few new conquests, and should imperil those we have already won. Men do not rest content with parrying the attacks of a superior, but often strike the first blow to prevent the attack being made.

And we cannot fix the exact point at which our empire shall stop; we have reached a position in which we must not be content with retaining but must scheme to extend it, for, if we cease to rule others, we are in danger of being ruled ourselves. Nor can you look at inaction from the same point of view as others, unless you are prepared to change your habits and make them like theirs.

Be convinced then that we shall augment our power at home by this adventure abroad, and let us make the expedition, and so humble the pride of the Peloponnesians by sailing off to Sicily, and letting them see how little we care for the peace that we are now enjoying; and at the same time we shall either become masters, as we very easily may, of the whole of Hellas through the accession of the Sicilian Hellenes, or in any case ruin the Syracusans, to the no small advantage of ourselves and our allies.

The faculty of staying if successful, or of returning, will be secured to us by our navy, as we shall be superior at sea to all the Siceliots put together.