History of the Peloponnesian War

"Then in the studies of war we excel our enemies in this. We leave our city open to all men; nor was it ever seen that by banishing of strangers we denied them the learning or sight of any of those things which, if not hidden, an enemy might reap advantage by, not relying on secret preparation and deceit but upon our own courage in the action. They, in their discipline, hunt after valour presently from their youth with laborious exercise, and yet we that live remissly undertake as great dangers as they. For example, the Lacedaemonians invade not our dominion by themselves alone but with the aid of all the rest.

But when we invade our neighbours, though we fight in hostile ground against such as in their own ground fight in defence of their own substance, yet for the most part we get the victory.