he Lernaean Hydra or Hydra of Lerna, more often known simply as the Hydra, was an ancient serpentine water monster with reptilian traits in Greek and Roman mythology. Its lair was the lake of Lerna in the Argolid, which was also the site of the myth of the Danaids. Lerna was reputed to be an entrance to the Underworld and archaeology has established it as a sacred site older than Mycenaean Argos. The Hydra served as a guard.
According to Hesiod, the Hydra was the offspring of Typhon and Echidna. It possessed many heads "more than the vase-painters could paint" and, each time one was lost, it was replaced by two more. It had poisonous breath and blood so virulent that even its scent was deadly. The Hydra was killed by Heracles as the second of his Twelve Labors.
The Hydra had many parallels in ancient Near Eastern religions. In particular, Sumerian, Babylonian, and Assyrian mythologycelebrated the deeds of the war and hunting god Ninurta, whom the Angrim credited with slaying 11 monsters on an expedition to the mountains, including a seven-headed serpent (possibly identical with the Mushmahhu) and Bashmu, whose constellation (despite having a single head) was later associated by the Greeks with the Hydra. The constellation is also sometimes associated in Babylonian contexts with Marduk's dragon, the Mushhushshu.