The gargoyle has a religious meaning. It's the guardian of the medieval cathedrals. Most of the time a monster, or a mythical animal, its task is to frighten bad spirits who could want to enter the church. It's supposed that the evil spirits will be terrorized by their own appearance.

It's also typical in the Middle-Age to represent what one wants to get rid of. Good examples of that state of mind are the feast of fools or the charivaris: one day in the year one destroys the "normal" world in a ritual that shows everything that's forbidden. Then the world can be rebuilt on new, safe foundations. The temporary image of evil conjures itself.

Oops... I forgot: of course a gargoyle is a gutter and nothing else.