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. Herakles 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.
- Graves, Robert (1960), The Greek Myths, Penguin Books, pp. 469–72