A corbel is a weight-bearing element or bracket placed deeply into a wall such that the pressure on its embedded section counteracts any propensity to topple or fall outward. Because of the corbel's beak-like appearance, the name is derived from a French term that means "crow." The corbels are usually made of wood and set closely together within the wall to provide extra support for the roof. As well as acting as structural elements, they often function as decorative features too. The corbelled style is an architectural form characterized by deep overhangs and heavy corbels. This style originated in France during the 11th century and was popular throughout much of Europe. It had fallen out of favor by the early 20th century but has since become popular again. There are two types of corbelled houses: those with flat roofs and those with sloping roofs. With respect to the first type, the roof is composed of flat surfaces supported by wooden beams and lined with waterproof material. There may be a parapet around the edge to provide protection against falling objects. These roofs do not leak even if it rains heavily for weeks at a time. Leaks will only occur if there is a hole in the roof covered by just a piece of paper or cloth. The second type of corbelled house has a sloping roof. This requires more complex construction because the walls need to follow the contour of the roofline.