A wall is a usually solid structure that separates space in buildings into rooms, or protects or delineates a space in the open air. Walls have two main purposes: to support roofs and ceilings, and to divide space, providing security against intrusion and weather.
Before the invention of artillery, many European cities had protective walls. Since they are no longer relevant for defense, the cities have grown beyond their walls, and many of the walls have been torn down.
The term "the Wall" frequently referred to the Berlin Wall, erected during the Cold War, which fell in 1989.
See also: List of walls, The Wall, Wallpaper, Dike (construction).