1911 Encyclopædia Britannica/Alcmaeonidae
ALCMAEONIDAE, a noble Athenian family, claiming descent from Alcmaeon, the great-grandson of Nestor, who emigrated from Pylos to Athens at the time of the Dorian invasion of Peloponnesus. During the archonship of an Alcmaeonid Megacles (?632 B.C.), Cylon, who had unsuccessfully attempted to make himself "tyrant," was treacherously murdered with his followers. The curse or pollution thus incurred was frequently in later years raked up for political reasons; the Spartans even demanded that Pericles should be expelled as accursed at the beginning of the Peloponessian war. All the members of the family went into banishment, and having returned in the time of Solon (594) were again expelled (538) by Peisistratus (q.v.). Their great wealth enabled them during their exile to enhance their reputation and secure the favour of the Delphian Apollo by rebuilding the temple after its destruction by fire in 548. Their importance is shown by the fact than Cleisthenes, tyrant of Sicyon, gave his daughter Agariste in marriage to the Alcmaeonid Megacles in preference to all the assembled suitors after the undignified behaviour of Hippocleides. Under the statesman Cleisthenes (q.v.), the issue of this union, the Alcmaeonids became supreme in Athens about 510 B.C. To them was generally attributed (though Herodotus disbelieves the story—see Greece, Ancient History, sect. "Authorities," II.) the treacherous raising of the shield as a signal to the Persians at Marathon, but, whatever the truth of this may be, there can be little doubt that they were not the only one of the great Athenian families to make treasonable overtures to Persia. Pericles and Alcibiades were both connected with the Alcmaeonidae. Nothing is heard of them after the Peloponessian war.
See Herodotus vi. 121-131.