A fire escape is a special kind of emergency exit, usually mounted to the outside of a building or occasionally inside but separate from the main areas of the building. It provides a method of escape in the event of a fire or other emergency that makes the stairwells inside a building inaccessible. Fire escapes are most often found on multiple-story residential buildings, such as apartment buildings. At one time, they were a very important aspect of fire safety for all new construction in urban areas; more recently, however, they have fallen out of common use. With the urban sprawl and increase in the amount of construction in the mid-20th century, particularly the increase in public housing in major cities in the United States and Europe in the 1950s and 1960s, certain problems with fire escapes became clear. In the poorer areas of cities like Chicago and New York, fire escapes were commonly used for everything but their intended purpose. In the hot summer months, residents of mid-rise apartment buildings would sleep outside on the platforms of their fire escapes. Such a situation triggered the plot premise of Cornell Woolrich's 1947 short story, "The Boy Cried Murder," about a boy on a fire escape who one night witnesses a murder in a neighboring apartment; this story was filmed as the suspense thriller The Window (1949). The practice of sleeping on fire escapes can also be seen in Alfred Hitchcock's 1954 movie Rear Window (also based on a Woolrich short story), as well as Weegee's photography of the Lower East Side). Diagonal shadows of fire escapes made them a constant motif in film noir, and the balcony scene of Romeo and Juliet was transposed to a fire escape for the musical West Side Story.