History of the Peloponnesian War

"But that it is you, [Plataeans,] who have both done more injury to Greece, and are more deserving of extreme punishment, we will now attempt to prove. It was for vengeance against us, you say, that you became allies and fellow-citizens of the Athenians.

Then you ought to have introduced them for aid against us alone, and not to have joined with them in attacking others; such a course having certainly been open to you, in case of your being at all led on by the Athenians against your will, since the confederacy against the Mede had already been formed by these Lacedaemonians here, which you yourselves bring forward most prominently [in your own defence]. Surely this was strong enough to divert us from attacking you, and, what is the greatest advantage, to enable you to take counsel in security. But of your own accord, and not by compulsion, you still took the part of the Athenians by preference.

And you say that it had been base for you to betray your benefactors; but much more base and criminal was it so utterly to betray the whole body of the Greeks, with whom you confederated, than to give up the Athenians alone, who were enslaving Greece, while the others were its liberators.

And it was no equal return of favour that you made them, nor one free from disgrace. For you introduced them, as you say, when you were being injured; but you became co-operators with them in injuring others. And yet not to return equal favours is more disgraceful than to fail in those which, though justly due, will be returned in furtherance of injustice.