In Greek mythology, the Hydra was a giant water snake with many heads that lived in a swamp near Lerna in the land of Argos. The number of heads is variously reported from as few as 5 to more than 100.

The second of the 12 labors of HerculesGreek hero who had 12 labors to perform; Roman god of strength 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 immortalable to live forever head. 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...