Athamas the Minyan, a founder of Halos in Thessaly but also king of the city of Orchomenus in Boeotia (a region of southeastern Greece), took as his first wife the cloud goddess Nephele. They had two children, the boy Phrixus (whose name means "curly"—as in ram's fleece) and the girl Helle. Later Athamas became enamored of and married Ino, the daughter of Cadmus. When Nephele left in anger, drought came upon the land.

Ino was jealous of her stepchildren and plotted their deaths: in some versions, she persuaded Athamas that sacrificing Phrixus was the only way to end the drought. Nephele, or her spirit, appeared to the children with a winged ram whose fleece was of gold. The ram had been sired by Poseidon in his primitive ram-form upon Theophane, a nymph and the granddaughter of Helios, the sun-god. According to Hyginus, Poseidon carried Theophane to an island where he made her into an ewe, so that he could procreate with her among the flocks. There Theophane's other suitors could not distinguish the ram-god and his consort.

Nepheles' children escaped on the winged ram over the sea, but Helle fell off and drowned in the strait now named after her, the Hellespont. The ram spoke to Phrixus, encouraging him, and took the boy safely to Colchis (modern-day Georgia), on the easternmost shore of the Euxine (Black) Sea.

There Phrixus sacrificed the winged ram to Poseidon, essentially returning him to the god. The ram became the constellation Aries.

Phrixus settled in the house of Aeetes, son of Helios the sun god. He hung the Golden Fleece reserved from the sacrifice of the ram on an oak in a grove sacred to Ares, the god of war and one of the Twelve Olympians. The golden fleece was defended by bulls with hoofs of brass and breath of fire. It was also guarded by a never sleeping dragon with teeth which could become human soldiers when planted in the ground. The dragon was at the foot of the tree on which the fleece was placed

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