Alkmaion’s father Amphiaraos, being a seer (mantis), foreknew that the expedition of the Seven Against Thebes would be a failure and that he, if he went on it, would never come back, indeed that no leader save Adrastos would ever return. Knowing also that Polyneikes would try to enlist the persuasions of his wife, Eriphyle, he forbade her to accept any gift from that quarter. She, however, disobeyed him, was bribed with the necklace of Harmonia, and at last won her husband to join the ill-fated enterprise. Departing reluctantly, he laid on his children the charge that they should avenge his death on their mother, and also that they should themselves make an expedition against Thebes [i.e., join the Epigonoi] when their time came. Thus occurred the Revenge of Alkmeon (or Alkmaion), who, in accordance with his father’s command, and like Orestes, killed his mother. The result of matricide for Alkmaion was similar to the result for Orestes; pursued from place to place by the Erinyes, although Apollo had formally approved his action and favoured him, after a time he came to Psophis in Arkadia, where Phegeus, king of that place, purified him and gave him his daughter Arsinoë in marriage. But famine fell on the country, and Alkmeon was bidden to seek a land on which the sun had not shone when he killed his mother.
This he found at the mouth of the river Acheloös, which had recently formed new land from the silt it bore seawards; there Alkmaion settled, and wed Kallirhoë, daughter of the river god. As his new wife longed for the necklace and robe of Harmonia (the latter, according to Apollodoros, had also been given to Eriphyle, to induce her son to go with the Epigonoi, a doublet of the story concerning the necklace), he got them from Phegeus by a trick; this being found out, he was set upon and killed by the latter’s sons, at the command of their father.
Arsinoë, who protested, was put into a chest, taken to Tegea, and given as a slave to Agapenor, king of Arkadia. But Kallirhoë begged Zeus, who was her lover, to cause her sons by Alkmeon, Akarnan and Amphoteros, to grow immediately to manhood. This was granted her, and the young men killed the sons of Phegeus, then Phegeus himself and his wife; after which they reported their doings to their mother, dedicated the robe and necklace to Apollo at Delphoi (where, according to later legends, the latter was stolen during the Phokian or Sacred War and brought nothing but ill luck to the thief), and then, gathering a band of followers, founded the land known in later ages as Akarnania.