In architecture, a gargoyle is a carved stone grotesque with a spout designed to convey water from a roof and away from the side of a building. Preventing rainwater from running down masonry walls is important because running water erodes the mortar between the stone blocks. Architects often used multiple gargoyles on buildings to divide the flow of rainwater off the roof to minimize the potential damage from a rainstorm. A trough is cut in the back of the gargoyle and rainwater typically exits through the open mouth. Gargoyles are usually an elongated fantastic animal because the length of the gargoyle determines how far water is thrown from the wall. When Gothic flying buttresses were used, aqueducts were sometimes cut into the buttress to divert water over the aisle walls.
A French legend that sprang up around the name of St. Romanus ("Romain") (AD 631–641), the former chancellor of the Merovingian king Clotaire II who was made bishop of Rouen, relates how he delivered the country around Rouen from a monster called Gargouille or Goji. La Gargouille is said to have been the typical dragon with batlike wings, a long neck, and the ability to breathe fire from its mouth. There are multiple versions of the story, either that St. Romanus subdued the creature with a crucifix, or he captured the creature with the help of the only volunteer, a condemned man. In each, the monster is lead back to Rouen and burned, but its head and neck would not, due to being tempered by its own fire breath. The head was then mounted on the walls of the newly built church to scare off evil spirits, and used for protection.