A gargoyle was originally a device mounted on the outside of a building to funnel water away from the roof. The word comes from the French "gargouille" which means "throat or pipe." This idea originated long ago, as samples of gargoyles have been found from ancient Greece.
Early gargoyles (the late 1200s) were carved wooden or stone channels, mostly undecorated. The carved variety became more common in medieval times, particularly in France on expensive or religious buildings, and fantastic creatures began to be the shapes preferred. The myth that gargoyles could ward off evil spirits and protect a building was born, and the carvings became even more grotesque and frightening.
Why were gargoyles so prevalent on cathedrals and prestigious buildings? Was it just a building fad? Some art historians from the middle ages believe that gargoyles represented evil beings over which the Christian church had triumphed. Some churches represented these carvings as devils who had been frozen in stone as they fled the righteousness of Christ. Psychologists believe that gargoyles may have represented the fears and superstitions of medieval times, noting that as life became easier and less fearful, gargoyles became less evil-looking and more playful.
Gargoyles eventually became ornamental rather than functional. Few of the gargoyles created after 1400 actually served as a rainwater channel. Many buildings constructed in the 1800s and early 1900s featured fantastic carvings. Many universities have lots of gargoyles. "Gargoyle hunting" has become a popular hobby among photographers, who comb downtown buildings and older residential areas for fantastic carvings to photograph. There's even a popular coffee table book called Nightmares in the Sky featuring photographs by f-stop Fitzgerald (come on now, how can you resist that name?) with text by Stephen King. Modern stone carvers will create a gargoyle for your garden or house to your specifications. "Garden Gargoyles" are even being sold as a common lawn ornament.