In Greek mythology the Hydra, which was also called Lernaean Hydra, is a serpent-like monster. According to Theogony 313, the hydra is the child of Typhon and Echidna. Hercules kills the Hydra as one of his Labors. The Hydra lived in the lake of Lerna in the Argolid. Under the lake was an entrance to the Greek underworld, which it guarded. The lake itself is older even than the Mycenean city of Argos. Lerna was the site of the myth of the Danaids, too. The Hydra is a nine-headed serpent like snake. It was said that if you cut one hydra head, two more grow back. And the middle hydra head breathes fire.
The second of the 12 labors of Hercules was to kill the Hydra. However, when one of the Hydra's heads was cut off, two more grew in its place. The monster also had one immortalhead. To defeat the Hydra, Hercules called on his friend Iolaus for help. As soon as Hercules cut off one head, Iolaus would seal the wound with a hot iron or a torch so that nothing could grow to replace it. After removing the Hydra's immortal head, Hercules buried it under a large rock. He then collected the monster's poisonous blood. In later adventures, he dipped his arrows in the blood so that they would instantly kill whomever they struck.