Alcmaeonidae, a noble family at Athens, members of which fill a space in Greek history from 1100 to 400 BC.
The Alcmaconidae were a branch of the family of the Neleidae. The Neleidae were driven out of Pylus in Messenia by the Dorians, about 1100 BC., and went to Athens, where Melanthus, the representative of the elder branch of the family became king, and Alcmaeon, the representative of the second branch,became a noble and the ancestor of the Alcmaeonidae. Alcmaeon was the great-grandson of Nestor. (Paus. ii. 18. § 7.) Among the archons for life, the sixth is named Megacles, and the last Alcmaeon. But, as the archons for life appear to have been always taken from the family of Medon, it is probable that these were only Alcmaeonids on the mother's side. The first remarkable man among the Alcmaeonids was the archon Megacles, who brought upon the family the guilt of sacrilege by his treatment of the insurgents under Cylon. (612 BC) The expulsion of the Alcmaeonids was now loudly demanded, and Solon, who probably saw in such an vent an important step towards his intended reforms, advised them to submit their cause to a tribunal of three hundred nobles. The result was that they were banished from Athens and retired to Phocis, probably about 596 or 595 BC. Their wealth having been augmented by the liberality of Croesus to Alcmaeon, the son of Megacles, and their influence increased by the marriage of Megacles, the son of Alcmaeon, to Agariste, the daughter of Cleisthenes, tyrant of Sicyon, they took advantage of the divided state of Athens, and by joining the party of Lycurgus, they effected their return; and shortly afterwards, by a similar union, they expelled Peisistratus soon after he had seized the government. ( 559 BC) This state of things did not last long; for, at the end of five years, Megacles gave his daughter Coesyra in marriage to Peisistratus, and assisted in his restoration to Athens. But a new quarrel immediately arose out of the conduct of Peisistratus towards his wife, and the Alcmaeonids once more expelled him. During the following tell years, Peisistratus collected an army, with which he invaded Attica, and defeated the Alcmaeonids, who were now once more driven into exile. They were, however, still formidable enemies.
After the death of Hipparchus, they took possession of Lipsydicum, a fortress on the frontier of Attica, and made an attempt to restore themselves, but were defeated by Hippias. They had, however, a more important source of influence. In the year 548 BC the temple of Apollo at Delphi was burnt, and the Alcmaeonids having contracted with the Amphictyonic council to rebuild it, executed the work in a style of magnificence which much exceeded their engagement. They thus gained great popularity throughout Greece, while they contrived to bring the Peisistratids into odium by charging them with having caused the fire. The oracle, besides, favoured them thenceforth; and whenever it was consulted by a Spartan, on whatever matter, the answer always contained an exhortation to give Athens freedom; and the result was that at length the Spartans expelled Hippias, and restored the Alcmaeonids. (510 BC) The restored family found themselves in an isolated position, between the nobles, who appear to have been opposed to them, and the popular party which had been hitherto attached to the Peisistratids. Cleisthenes, now the head of the Alcmaeonidae, joined the latter party, and gave a new constitution to Athens. Further particulars respecting the family are given under the names of its members. (Herod. vi. 121-131; Pindar, Pyth. vii., and Böckh's notes; Clinton's Fasti, ii. p. 4, 299.)