The Kibisis was born not in a forge but in a gift. When Perseus stood on the shore of Seriphos, the island where he had been raised by the fisherman Dictys, and learned that King Polydectes had sent him to fetch the head of the Gorgon Medusa, he knew he could not face the quest alone. The Gorgons lived at the western edge of the world, beyond the known lands, in a place where the sun set into the ocean. Medusa was one of three sisters, daughters of the sea gods Phorcys and Ceto, and her face was so terrible that one look turned living things to stone. She had once been a beautiful maiden who had lain with Poseidon, the god of the sea, in a temple of Athena, the goddess of wisdom and war, and Athena had transformed her hair into serpents and her face into a weapon. Perseus was a young man with courage but no experience, and the quest was meant to kill him.

But the gods took pity on him, or perhaps Athena saw a chance to undo some of the harm her curse had caused. The nymphs who guarded the treasures of the gods came to Perseus with four gifts. They gave him the winged sandals of Hermes, the messenger god, which carried their wearer across the earth and sea faster than any bird. They gave him the cap of darkness, the helm of Hades that rendered its wearer invisible even to the gods themselves. They gave him the harpe, the curved blade of adamant that had once castrated the Titan Uranus and that no mortal smith could forge. And they gave him the kibisis, a leather bag or wallet, simple and strong, with a cord to cinch it tight. It was not a weapon. It was not armour. It was just a bag, but it was the bag that would hold the Gorgon's head, and without it the quest would have ended the moment the head was severed, for Perseus could not have carried the face that turned men to stone without being turned himself.

Perseus flew west on his winged sandals, invisible in the cap of Hades, and found the Gorgons sleeping in their cave, the serpents of Medusa's hair hissing and coiling in their dreams. He approached with a polished bronze shield given by Athena, using it as a mirror to see Medusa's reflection without looking directly at her face, and when he stood over her he raised the harpe and brought it down in a single sweeping stroke. The blade cut through the serpent locks and the immortal flesh beneath, and Medusa's head fell from her body. From the stump of her neck sprang Pegasus, the winged horse, and Chrysaor, the warrior with the golden sword. Perseus did not pause to marvel. He snatched up the head by its snaky hair, dropped it into the kibisis, and cinched the cord tight. The bag held the face that turned men to stone, and the leather did not turn to stone, and Perseus was safe.

The kibisis proved its worth on the journey home. Perseus flew over Libya, and drops of blood from the Gorgon's head, still wet inside the bag, fell upon the sand and turned into venomous serpents that have infested the desert ever since. He came to the land of the Aethiopians, where the princess Andromeda had been chained to a rock as a sacrifice to a sea monster sent by Poseidon, the god of the sea, because her mother Cassiopeia had boasted that she was more beautiful than the Nereids, the sea nymphs who attended Poseidon's wife Amphitrite. The monster rose from the waves, vast and scaled, and Perseus saw Andromeda weeping on the rock. He flew down, opened the kibisis, and held the Gorgon's head toward the beast. The monster froze in an instant, turned to solid stone where it stood in the shallows, and Perseus cut Andromeda's chains and claimed her as his bride. The bag had turned a sea monster into a reef with a single glance.

The kibisis appears one last time in the story of Perseus's return to Seriphos. He arrived to find that King Polydectes, who had sent him on the fatal quest to clear the way for his own pursuit of Danae, had grown violent in his demands. Polydectes had assembled his whole court and was threatening Perseus's mother when the hero walked in. Perseus asked the king why he had sent him to die, and Polydectes laughed and called him a liar, saying no man could have slain the Gorgon. Perseus reached into the kibisis, pulled out the head, and turned Polydectes and every man in the hall to stone where they stood. The tyrant who had thought himself safe behind his throne was petrified in his own chair, his hand still raised in command, his mouth still open in mockery. Perseus then gave the head to Athena, the goddess of wisdom and war, who fixed it upon her shield, the aegis, where it would turn her enemies to terror forever. The kibisis, its work done, returned to obscurity.

What became of the bag itself, the old stories do not say. Some say Perseus kept it as a heirloom, the wallet that had carried the most terrible object in the world and survived. Others say the nymphs took it back, for divine gifts are often loans rather than possessions. But the idea of the magical bag, the container that holds more than it should or protects its bearer from what it contains, passed from Greek myth into the medieval imagination and then into the modern world. The wallet that holds a fortune, the sack that carries a giant's treasure, the bag of holding in every role-playing game, all descend from the simple leather kibisis that Perseus cinched tight around the Gorgon's snaky hair.

In later art, the kibisis is often shown at Perseus's side, a small bag hanging from his belt or held in his hand, unremarkable beside the winged sandals and the harpe. But its presence is essential, for without it the hero could not have brought his trophy home. Greek vase painters from the sixth century BCE onward showed Perseus with the bag, and Roman sculptors placed it in the hands of every image of the Gorgon-slayer. The bag became a symbol of preparedness, of the humble tool that makes the impossible possible, and of the truth that even the greatest heroes need something to carry their prizes in.