History of the Peloponnesian War
Thucydides
Thucydides, Vol. 1-4. Smith, Charles Foster, translator. London and Cambridge, MA: Heinemann and Harvard University Press, 1919-1923.
"We will now try to show that you Plataeans have wronged the Hellenes more than we and are more deserving of any punishment, however severe. You became allies and citizens of Athens that you might, as you claim,[*](cf. 3.55.1.) obtain protection against us.
In that case you ought only to have invoked their aid against us, instead of assisting them in their aggressions against others; such a course was certainly open to you, in case you were ever being led on by the Athenians against your will, since the alliance of the Lacedaemonians here had already been organized against the Persians—the alliance of which you are always reminding us.[*](The alliance of the Lacedaemonians that is in mind here would seem to be the general league of the Hellenes in the Persian War, in which the Lacedaemonians were leaders; but in 3.58.1 the Plataeans use the words θεῶν τῶνξυμμαχικων ποτε γενομένων especially with reference to the compact mentioned in 2.71, where it is said that the allies, at the instance of Pausanias, after the battle of Plataea, mutually guaranteed the independence of all the Hellenic states, and of the Plataeans in particular.) That would have been enough to keep us from interfering with you, and, what is more important, to enable you to take your own counsel without fear. Nay, it was willingly and not now under compulsion that you embraced the Athenian cause.
You say, however, that it would have been dishonourable to betray your benefactors; but it was far more dishonourable and wicked to betray to their destruction all the Hellenes, with whom you had sworn alliance, than merely the Athenians, when they were endeavouring to enslave Hellas, the others to liberate her.