Prophylaxis

Walter de Chepe's Prophylaxis "protects a person, city or object from magic spells", however it frequently takes a much stronger effect than desired, so much so that "objects become impervious to human or fairy agency of any sort whether magical or not."[50]

In 1280, the spell was cast on the town of Bristol with the intent of protecting the community from spells, but was so powerful that nothing and no-one within the town's boundaries was able to move at all until the Raven King came south in person to remedy matters [50]. Prophylaxis — the word generally means the prevention of disease — is apparently based on a piece of fairy magic.

See also Prophylactics against magic