In Greek mythology, Amphiaraus (or Amphiaraos, "doubly-cursed" or "twice Ares-like) was the son of Oecles and Hypermnestra, and husband of Eriphyle. Amphiaraus was the King of Argos along with Adrastus— the brother of Amphiaraus' wife, Eriphyle— and Iphis. Amphiaraus was a seer, and greatly honored in his time. Both Zeus and Apollo favored him, and Zeus gave him his oracular talent. In the generation before the Trojan War, Amphiaraos was one of the heroes present at the Calydonian Boar Hunt.
The material of the tragic war of the Seven Against Thebes was taken up from several points-of-view by each of the three great Greek tragic poets. Eriphyle persuaded Amphiaraus to take part in the raiding venture, against his better judgment, for he knew he would die. She had been persuaded by Polynices, who offered her the necklace of Harmonia, daughter of Aphrodite, once part of the bride-price of Cadmus, as a bribe for her advocacy. Amphiaraus reluctantly agreed to join the doomed undertaking, but aware of his wife's corruption, asked his sons, Alcmaeon and Amphilochus to avenge his inevitably coming death by killing her, should he not return. On the way to the battle, Amphiaraus repeatedly warned the other warriors that the expedition would fail, and blamed Tydeus for starting it. He would eventually prevent Tydeus from being immortalized by Athena because of this. Despite this, he was possibly the greatest leader in the attack. During the battle, Amphiaraus killed Melanippus. In the battle, Amphiaraus sought to flee from Periclymenus, the "very famous son of Poseidon, who wanted to kill him, but Zeus threw his thunderbolt, and the earth opened to swallow Amphiaraus together with his chariot. Thus chthonic hero Amphiaraus was propitiated and consulted at his sanctuary.
Alcmaeon killed his mother when Amphiaraus died. He was pursued by the Erinyes as he fled across Greece, eventually landing the court of King Phegeus, who gave him his daughter Alphesiboea in marriage. Exhausted, Alcmaeon asked an oracle how to avoid the Erinyes and was told that he needed to stop where the sun was not shining when he killed his mother. That was the mouth of the river Achelous, which had been silted up. Achelous himself, god of that river, promised him his daughter, Callirhoe in marriage if Alcmaeon would retrieve the necklace and clothes which Eriphyle wore when she persuaded Amphiaraus to take part in the battle. Alcmaeon had given these jewels to Phegeus who had his sons kill Alcmaeon when he discovered Alcmaeon's plan.
In a sanctuary at the Amphiareion of Oropos, northwest of Attica, Amphiaraus was worshipped with a hero cult. He was considered a healing and fortune-telling god and was associated with Asclepius. The healing and fortune-telling aspect of Amphiaraus came from his ancestry: he was related to the great seer Melampus. After making a sacrifice of a few coins, or sometimes a ram, at the temple, a petitioner slept inside and received a dream detailing the solution to the problem.
Etruscan tradition inherited by the Romans is doubtless the origin of a son for Amphiaraus named Catillus who escaped from the slaughter at Thebes and led an expedition to Italy, where he founded a colony where eventually appeared the city of Tibur (now Tivoli), named after his eldest son Tiburtus.
In certain traditions he was said to have had a daughter, Alexida.