wall, in architecture, protective, enclosing, or dividing vertical structure. Its thickness is determined by the material, height, and stress. It may be of studding and lath, either boarded or plastered; adobe; rammed earth; brickwork or stonework; concrete; tile; or of steel in combination with one or more of the preceding materials. The wall serves two functions. A bearing wall is used as a support, e.g., for the floors and roof. Usually raised on foundations, it is thicker at the bottom than at the top and is often buttressed. A nonbearing wall, such as a partition screen or curtain wall, is used to separate and define spaces and is generally much thinner. A party wall is one common to two adjoining buildings, and a gable wall is one at right angles to the roof ridge. A fire wall, or bulkhead, separates hazardous equipment from the rest of a structure to prevent the spreading of fire; in ships the bulkhead is also watertight. The front wall or face of a building is termed the facade. Exterior walls may be finished with stucco or graffito and enhanced by bas-relief, tile, mosaic, or painted decoration. Arcade, rustication, and vermiculated work are means of ornamenting brick and stone masonry. In engineering a retaining wall either of Cyclopean or of wet masonry protects an embankment from washing; a sea wall, or breakwater, is for harbor protection; and a dam is an earth, masonry, or concrete wall to stop the natural flow of a stream to conserve a water supply or create power. The defensive walls of a city or other political division (see Great Wall of China) are frequently two or three concentric ramparts, often including fortification and watchtowers. Great portals form the gateways. Notable walls of antiquity were those of Thebes, Troy, Jericho, and Babylon; an example of a medieval wall is that at Carcassonne in France.