A man named Phrixus had flown on a magical golden ram—a gift from Hermes—to Colchis, the kingdom of Aeëtes at the eastern end of the Black Sea. There he had sacrificed the ram to Zeus and presented its fleece to King Aeëtes. The king had hung it on the branch of an oak tree in a place that was sacred to Ares and had assigned a never-sleeping dragon the job of guarding it.

Jason took up the challenge of obtaining the Fleece. This would be the quest which would establish his position as a true hero in the mode of Perseus, Herakles, and Theseus. First he built a sturdy ship, the Argo, and gathered a crew of “Argonauts” that included such powerful figures as Herakles, the greatest of Greek heroes, and Orpheus, the famous musician. Other heroes included in the crew were Peleus, father of Achilles, and Castor and Polydeuces (Pollux)—the twins known as the Dioscuri, literally meaning “sons of god,” because they were products with Helen and Clytemnestra of the union between Leda and Zeus (as a swan). The adventures surrounding the quest are related in the Argonautica of Apollonius of Rhodes.