Acastus
King of Iolcus and Argonaut who tried to murder Peleus through treachery on Mount Pelion — a tale of false accusation and sacred hospitality violated.
The Legend of Acastus
Acastus was a king of Iolcus in Thessaly, son of Pelias and one of the Argonauts who sailed with Jason in search of the Golden Fleece. His story is one of betrayal, false accusation, and divine vengeance — a pattern repeated throughout Greek mythology but given particular force in the tale of his conflict with the hero Peleus.
After the death of his father Pelias — killed through the trickery of Medea — Acastus inherited the throne of Iolcus and held funeral games in his father's honour. According to Apollodorus, Peleus participated in these games and won great distinction. But Acastus's wife, Astydameia (or in some versions Hippolyte), fell in love with Peleus. When Peleus rejected her advances, she sent a message to his wife Antigone claiming that Peleus was about to marry Acastus's daughter. Antigone, believing the lie, hanged herself.
The Great Deeds
Still unsatisfied, Astydameia told Acastus that Peleus had tried to seduce her — a classic "Potiphar's wife" motif found in myths across cultures. Acastus could not kill a guest directly without violating the sacred laws of hospitality (xenia), so he devised a subtler plan. He took Peleus hunting on Mount Pelion and, while Peleus slept, hid his sword — a divine blade forged by Hephaestus — and left him alone and unarmed among the centaurs.
The plan nearly worked. But according to Apollodorus, the centaur Chiron — the wise teacher of heroes — found Peleus and returned his sword, saving his life. Peleus later returned to Iolcus with an army. In some versions he killed both Acastus and Astydameia; in others, he dismembered Astydameia and marched his army through her remains as punishment for her deceit.
Trials and Tribulations
Acastus's story illustrates the Greek preoccupation with xenia — the sacred bond between host and guest. His failure was not in wanting revenge but in the cowardly, indirect means he chose. The gods rewarded Peleus for his virtue: he went on to marry the sea nymph Thetis, and their son was Achilles, the greatest warrior of the Trojan War.
Parents
Pelias, Anaxibia
Symbols
Fun Fact
Peleus survived Acastus's murder plot thanks to the centaur Chiron — and his reward for enduring the false accusation was marriage to the goddess Thetis, making him the father of Achilles. The worst day on Mount Pelion led directly to the greatest warrior of the Trojan War.
Words We Inherited
English words and phrases that trace back to this myth. See our full guide to English words from Greek mythology.
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