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.

And first the Lacedaemonian envoys bade the Athenians drive out the "curse of the goddess." The curse was as follows:

There was an Athenian in days of old named Cylon, a victor at Olympia, of noble birth and powerful; and he had married a daughter of Theagenes, a Megarian, who was at that time tyrant of Megara.

Now Cylon consulted the oracle at Delphi, and the god in answer told him to seize the Acropolis of Athens "at the greatest festival of Zeus."