Fluffy, the room-size, three-headed dog who guards the Philosopher's Stone at Hogwarts, has a mythological heritage dating back almost three thousand years. His most venerable ancestor is Cerberus, the savage hound of Greek and Roman legend who guards the entrance to the underworld. In the eighth century B.C., the poet Hesiod described Cerberus as having fifty heads and a voice of brass. Just two centuries later, however, fifty heads apparently seemed excessive even for a vicious guard dog. In what became the standard image of the beast, artists depicted Cerberus with a mere three heads, a dragon's tale, and a backbone that bristled with serpents.
      The ancient Greeks believed that when someone died, his or her spirit went to the world below. Ruled by the god Hades and his wife Persephone, this "underworld" was the destination of all souls, good or bad, but the quality of their lives there depended on how they had behaved on Earth. As the watchdog of the underworld, Cerberus' job was to make sure no one escaped the kingdom of Hades after passing through the gates. Born of two terrible monsters (his father was a fire-breathing giant covered in snakes and his mother a half-woman, half-serpent who ate men raw), Cerberus had little trouble frightening people. If the sheer sight of him was not enough, the sharp teeth of three wild dog's heads and the spikes in his tail could be used quite effectively.
      Only a few mythological characters managed to elude Cerberus and make the journey back to the land of the living. The nymph Psyche managed to sneak past by feeding the dog a drugged honey cake, and the Trojan war hero Aeneas followed her example. The musician Orpheus, who ventured into the underworld in search of his dead wife, Eurydice, played his lyre so beautifully that Cerberus closed his eyes in ecstasy and allowed him to pass (Fluffy reacts to music in much the same way). And Hercules, completing the last of his twelve labours, wrestled Cerberus with his bare hands, managing to drag the beast back up to Earth for a brief time.
      Legend holds that during his days in the world of the living, Cerberus drooled, as dogs will. A few drops of his saliva fell on the earth, from which sprang a poisonous plant called aconite. Also known as wolfsbane, aconite is a real plant that was commonly used in the potions and ointments of foth fictional and real witches.