When Hercules/Herakles killed his family in an insane rage, the oracle of Delphi assigned him a series of labors under the control of Eurystheus his cousin and king of Mycen�. The second labor involved going to Lerna to kill the hideous monster named the Hydra of Lerna.
The Hydra, born of Typhon and Echidna, was an enormous serpent with nine heads. Its den was a marsh near Lerna in Peloponnese. It would issue forth to ravage the herds and crops, its breath moreover was so poisonous that whoever smelt it fell dead.
With the help of Athene/Pallas (goddess of wisdom and prudent warfare), Hercules located the monster’s lair. Accompanied by Iolaus, son of his twin brother Iphicles, Hercules arrived at Lerna, found the monster near the spring of Amymone. and forced it to emerge from the marshes by means of flaming arrows.
Hercules struck it with his sword, but even as he parried, a giant crab (Cancer), sent by his enemy, Juno (the jealous and vindictive wife of Jupiter who was Hercules’ father), scurried out of the marsh and attacked him, by nipping his feet. Quickly Hercules kicked the crab away and with one almighty blow of his club pounded it to pieces. Every time Hercules struck off one of the Hydra nine heads with his sword two grew in its place.
Iolaus set the neighboring forest on fire. It was Iolaus who suggested burning the stumps before they had a chance to grow back; and with the help of a red-hot brand (torch or club – depending on the version), Iolaus burnt the snake’s heads, cauterizing each stump with hot iron torches just as soon as Hercules chopped off each head and before it had a chance to grow back.
With the blood flow stopped, the Hydra’s heads ceased to multiply. Hercules cut off the final head and buried it under a rock which can be found to this day on the road from Lerna to Elaeus. Then he soaked his arrows in the Hydra’s blood which made them poisonous and deadly. Even a grazing shot from one of those arrows would kill.
While one might be tempted to say “well done”, Eurystheus, who had assigned these labors to Hercules, was not satisfied. Hercules had cheated, he said, since he had needed Iolaus’ assistance. Upon completing this, which was his second labor, Hercules had acquired all of his famous armor with which he is usually depicted; the lion’s skin; the poisoned arrows; and the club that he made from the tree trunk he had used to burn the Hydra’s necks.