The Gorgons were born in the earliest days of the cosmos, before the Olympian gods had secured their throne, when monsters still walked the earth and the sea was a place of terror rather than commerce. Their father was Phorcys, the old man of the sea, a primordial deity who dwells in a cave at the bottom of the ocean with his wife Ceto, the goddess of the sea's darkest depths. Phorcys is half man and half fish, with crab-claw forelegs and red spiked skin, while Ceto is the very embodiment of the monstrous sea. Together they produced a family of horrors: the Graeae, three grey sisters born old who share one eye and one tooth between them; Echidna, the half-woman half-serpent mother of the Chimera, Cerberus, and the Hydra; Ladon, the hundred-headed dragon who guards the golden apples of the Hesperides; and the Gorgons themselves, three winged women whose beauty is a lie and whose gaze is death.

Hesiod, the poet who wrote the Theogony, the great genealogy of the gods, places the Gorgons far beyond the river Oceanus, the stream that encircles the entire world, in a place where night meets the western sun and the Hesperides, the nymphs of the evening, sing beside the golden tree. The island is called Sarpedon, a rocky place in deep-eddying water where no mortal ship has ever anchored. The Gorgons are described as winged, with round faces, large staring eyes, wide mouths, lolling tongues, the tusks of swine, flared nostrils, and serpents for hair. Their hands are brazen, their claws are golden, and their feet are swift. All who look upon them turn to stone, not from any magic spell but from the sheer terror of their visage, which freezes the blood in the veins and turns the heart to marble. Stheno and Euryale are immortal, ageless, and cannot die, but Medusa is mortal, a fact that would prove her undoing.

The later poets, especially Ovid in his Metamorphoses, told a different story about Medusa alone. In this version, Medusa was not born a monster but was once a beautiful maiden, a priestess of Athena who served in the goddess's temple with hair that was the envy of every woman in Greece. Poseidon, the god of the sea whose rivalry with Athena was ancient and bitter, desired her and lay with her in the very temple of the goddess, a double offence against Athena's virgin dignity and her sacred space. When Athena discovered the desecration, she could not punish Poseidon, who was her uncle and equal in power, so she turned her wrath upon Medusa. She transformed the maiden's beautiful hair into a nest of writhing serpents, changed her face into the mask of terror that would turn any viewer to stone, and made her a monster who would be shunned by gods and men alike. Some say this curse extended to her sisters as well, making all three into the Gorgons we know, though the older accounts maintain they were born monsters from the beginning. Whether cursed or born, the result was the same: three sisters who lived in isolation, shunned by all, deadly to any who approached.

The hero Perseus, the demigod son of Zeus and the princess Danae, was sent to fetch the head of Medusa by King Polydectes of Seriphos, an island in the Aegean Sea. Polydectes desired Perseus's mother Danae and wanted the hero out of the way, so he demanded the impossible gift as the price of his forbearance. The gods, knowing that Polydectes was a tyrant and that Perseus was destined for greatness, equipped the hero with divine weapons. Athena, the goddess whose rivalry with Poseidon had created Medusa's curse, gave him a polished bronze shield that shone like a mirror. Hermes, the messenger of the gods who wore winged sandals and carried a wand that could charm any creature, gave him a pair of those same winged sandals and a curved sickle of adamant, the unbreakable metal of the gods. Hades, the gloomy king of the underworld, gave him the helmet of darkness, a cap that made the wearer invisible to gods and men alike. The Graeae, the Gorgons' sisters, revealed the location of the nymphs who possessed the kibisis, a special wallet of woven silver and gold in which the severed head could be carried without killing the bearer.

Perseus flew across the western ocean, past the Hesperides and the pillars that hold the sky, until he reached the island of the Gorgons. He found them sleeping, their serpent hair coiled upon the rock, their brazen claws relaxed, their terrible eyes closed. Stheno and Euryale lay on either side of their mortal sister, and all three were at rest in the midday heat. Perseus, guided by Athena, approached with his eyes fixed not on the monsters but on the reflection in his polished shield. He saw Medusa's image in the bronze, the terrible face made harmless by reflection, and with a single stroke of the adamant sickle he severed her head from her body. The moment the blade cut through her neck, two beings sprang from the wound: Pegasus, the winged horse whose name comes from the springs of Oceanus where the Gorgons were born, and Chrysaor, the golden warrior who carried a sword of blazing light and would one day father the triple-bodied giant Geryon. Medusa's blood, spilled upon the rocks and the seaweed of the shore, was said to have created the coral reefs of the Red Sea and the venomous vipers of the Sahara desert, so potent was the poison in her veins.

The noise of the beheading woke Stheno and Euryale. They rose with shrieks that shook the island, their wings beating the air, their serpent hair hissing in fury, their brazen claws reaching for the killer of their sister. But Perseus had already seized the severed head, placed it in the kibisis, and donned the helmet of Hades. He was invisible, a shadow in the wind, and though the immortal sisters pursued him across the sky, their claws grasping at empty air and their shrieks echoing across the western ocean, they could not find him. He flew eastward, past the Atlas Mountains where he would later turn the Titan Atlas to stone with the head, past the kingdom of Aethiopia where he would save Andromeda from the sea monster Cetus, and back to Seriphos where he would turn Polydectes and his court to stone for their tyranny.

The head of Medusa became the most powerful weapon in Greek mythology. Perseus gave it to Athena, the goddess who had guided his hand, and she placed it upon her aegis, the breastplate or shield that she wore in battle. From that day forward, any enemy who looked upon Athena's shield turned to stone before her spear could strike, and the image of the Gorgon's face, called the Gorgoneion, became the most feared and revered symbol in the Greek world. It appeared on the shields of warriors, on the walls of temples, on the prows of ships, and on the breastplates of heroes. The Athenians believed that the head of Medusa was buried beneath a mound in the Agora, the central square of their city, where it served as a protective talisman against invasion. The Gorgoneion was not merely a weapon; it was an apotropaic device, a face that turned evil away, that protected the bearer by reflecting the malice of the enemy back upon them. Even in death, Medusa's face was a guardian, and her sisters Stheno and Euryale remained in their western fastness, immortal and terrible, mourning their sister and waiting for any fool who might dare to approach their island again.