In Greek legend, a gigantic monster with seven heads (in some other versions it has nine heads), of which the center one is immortal. It is the offspring of Typhon and Echidna. It haunted the marshes of Lerna near Argos. Heracles managed to kill the Hydra with the help from his cousin Iolaos. Each time they had cut a head off, two new ones grew back on so they scorched the wounds with burning branches to prevent this. Heracles dipped the tips of his arrows in the poisonous blood of the Hydra; those arrows, when fired, would cause incurable wounds. The destruction of the Hydra was the second of the Twelve Labors of Heracles. Virgil (VI,576) placed the Hydra in the underworld as a guardian.