Alcmeon, in Greek mythology, was a son of the diviner Amphiarau and Erifila, sister of King Adrasto.
Polynices was in Argos looking for warriors to fight his brother Aetocles and take Thebes, but Amphiarau, who had predicted his own death in the campaign, did not want to go. Polynices then gave Erifila the golden necklace that had been a gift from the goddess Athena to Harmonia, so that Erifila would convince her husband to join the war.
Amphiarau was in dispute with Adrasto over both who would be king of Argos and whether they would go to war with Thebes, and they took the decision to be made by Erifila, who gave Adrasto every reason. Amphiarau, feeling betrayed by his wife, gave orders to his son Alcmeam to kill Erifila if he did not return from the war.
During the war (the Seven Against Thebes), Amphiarau died when the earth opened up, swallowing the chariot he was in,
Ten years later, when the expedition of the Epigoni was being organized, Alcmeon consulted the oracle of Apollo about the campaign and about punishing his mother, and the oracle said that he should do both.
The oracle also said that the expedition would be successful if Alcmeon was the leader. Alcmeon learned that Erifile had received a garment from Tersander, son of Polynices, so that she could persuade him to join the expedition of the Epigoni.
Alcameon was the leader of the attack against Thebes, and his companions were Amphilochus the son of Amphiarchus, Egialeus the son of Adrastus, Diomedes the son of Tideus, Promachus the son of Parthenopeus, Phrenopus the son of Capaneus, Tersandus the son of Polynices, and Euryalus the son of Mecystheus.
The attack began against the neighboring villages of Thebes, which were devastated. The Thebans, led by Laodamante, son of Aetocles, faced them, and fought bravely.
Laodamante killed Aegealus, but was killed by Alcman, and after the death of their king the Thebans retreated behind the walls. Tyrethias advised them to negotiate with the Argives, and while his spokesman negotiated, the Thebans fled with their women and children.
After the capture of Thebes, upon learning that his mother had also been corrupted to send him against Thebes, Alcmeon killed her, and then went mad from guilty conscience. Some say that Alcmeon killed his mother alone, but others say that he killed along with his brother Amphilochus.
Pursued by the Furies, Alcmeon met with Oicles in Arcadia, and with Phegeus in Psophis. Phegeus purified him, and Alcmeon married Arsinoe, Phegeus' daughter, giving her the necklace and clothing as a gift.
After this, the land became barren, and the Oracle ordered Alcmaion to go to the river Aquelo, to be judged. On the way, Alcmaion visited Enneus in Chaldea and the thespians, but was driven out of the country, and went to the fountains of the Aquelo. The river-god purified him, and gave him his daughter Chalírroe as a wife. Alcmeon colonized the land near the river.
Chalírroe coveted the necklace and garment, and sent Alcmeon to Psophis, for him to tell Phegeus that he would only be freed from madness if he delivered the necklace and garment to the Oracle of Delphi.
Phegeus believed him, and delivered them, but a servant discovered that Alcmaeon would be taking the necklace to Chalírroe. Phegeus sent his sons, who killed Alcmen. Arsínoe accused them of murder, and they locked her in a chest and sent her as a slave to Agapenor, saying that she had killed Alcmeon.
Calírroe had had two sons with Alcmeon, Amphoterus and Acarnan, but they were minors. Calyrrhus asked Zeus, and Zeus caused them to become men, to avenge Alcmeon.
Amphoterus and Acarnan met Pronous and Agenor at Agapenor's house, when the latter were taking the necklace and clothes to Delphi. The sons of Alcmeon killed the sons of Phegeus, then went to Psophis and killed Phegeus and his wife. They fled, being pursued as far as Thegea, when they were saved by the Tegeans and some Argives.
According to Euripides, during his madness Alcmeon had a son, Amphilocus, and a daughter, Tisiphone, with Manto, daughter of Tyresias. The two sons, when they were babies, were taken to Corinth and raised by their king Creon. Since Tisiphone was very beautiful, Creon's wife sold her into slavery, for fear that she would become his wife.
But Alcameon ended up buying her, to be his servant, without knowing that she was his daughter. As he passed through Corinth, Alcameon also recovered his son. Amphilochus founded the city of Argos of Amphiloque.