In Ancient Greek myth, the Hydra of Lerna was an enormous, many-headed, snake-like sea monster that guarded the entrance to the Underworld. The Greek hero Hercules slayed the Hydra as the second of his twelve labours.
At the beginning of the nineteenth century, Europe's ruling classes were all rather unnerved by the recent French Revolution of 1789. Many were worried that the radical, violent defeat of the aristocracy in France would lead to similar liberal revolts in neighbouring countries. In reaction to this concern, surviving monarchies became increasingly authoritarian, and any hints of liberal or republican tendencies were treated with great suspicion, and were subject to violent repression.