ALCMAEONIDAE, a powerful Athenian family, which played a leading part in the politics of the 6th and 5th centuries, B.C. The murder of the Cylonian conspirators (c. 632) brought the pollution of blood-guilt on them (cf. esp. Hdt. v. 70-71 and Thuc. i. 126-127) and they were banished until the time of Solon. Alcmaeon seems to have made his fortune through the favour of the kings of Lydia. Megacles, who made a great marriage with the daughter of the ruler of Sicyon, led the merchant party in opposition to the tyrant Peisistratus, and was exiled (Hdt. i. 59) his son Cleisthenes drove out the tyrants (510), defeated the Spartan attempt to set up an oligarchy, and by his reforms secured the Athenian democracy. The Alcmaeonids were sus pected, however, of treacherously helping the Persians by giving the famous shield signal at Marathon. To the same family be longed Pericles and Alcibiades.
See Herodotus vi. 121-131, and articles on CLEISTHENES, PERICLES, ALCIBIADES, GRAECO-PERSIAN WARS and Camb. Anc. Hist. vol. iv. ch.
vi., § 6 and ch. viii.