The Graeae were born to Phorcys, the old man of the sea, and Ceto, the monstrous goddess of the deep. Hesiod, writing his Theogony around 700 BCE, names only two: Pemphredo, "she who shows the way," and Enyo, "the warlike." Apollodorus, writing his Library in the 2nd century BCE, adds a third, Deino, "the terrible," and Hyginus gives Persis, "the destroyer," as an alternative. They were grey-haired from birth, their faces pale as sea-foam, and they shared a single eye and a single tooth between them. The eye was passed from hand to hand so that each could see in turn, and the tooth was shared so that each could eat. They lived in a cave on the island of Cisthene, beyond the western edge of the known world, where the sun never shone.

The Graeae were keepers of a secret. They alone knew the location of the three magical objects that Perseus, the son of Zeus and the mortal Danae, would need to kill the Gorgon Medusa, a creature so terrible that one look at her face turned living things to stone. They also knew the path to the cave where the Gorgons lived, and the location of the nymphs who guarded the winged sandals, the cap of darkness, and the kibisis, the special bag that could hold a severed head. Perseus, sent on this quest by Polydectes, the king of Seriphos, traveled to the land of the Graeae and found them sitting in their cave, passing the eye between them.

Perseus watched from the shadows as the eye moved from one sister to another. When the moment came, he snatched the eye and held it in his hand. The Graeae cried out in terror, for without the eye they were blind, and without the tooth they could not defend themselves. They begged him to return it, but Perseus refused unless they told him where to find the nymphs who kept the magical objects. The sisters, desperate, revealed the secret. Some say Perseus returned the eye afterward and left them in darkness. Others say he threw it into Lake Tritonis and left them blind forever. In either case, the secret was out, and the path to Medusa was open.

The Graeae appear in one other famous tale. In Aeschylus' lost play The Phorcydes, they formed the chorus, swan-shaped creatures with the heads and arms of old women, singing of the doom that awaited their sister Medusa. Prometheus, the Titan who stole fire for mankind, warned the maiden Io of the dangers she would face on her wanderings, and named the Graeae among them: "ancient maids, three in number, shaped like swans, possessing one eye amongst them and a single tooth." They were personifications of the white foam on the waves, the grey scum that marks the edge of the sea, and their shared eye was the lamp that lit the boundary between the known world and the realm of monsters.

The image of three old women sharing a single eye has echoed through centuries. The Graeae appear in Clash of the Titans and countless retellings of the Perseus myth, always as the gatekeepers who must be tricked before the hero can face the Gorgon. Their names live on in the words "dread," "horror," and "alarm," the emotions they embodied. They are the ancient guardians of secrets, the embodiment of the old world's resistance to the new hero. Every quest that begins with a riddle, every journey that starts with a gatekeeper who must be outwitted, carries the memory of the grey sisters and their stolen eye.