fourth wall

In Stanislavski's production of The Cherry Orchard (Moscow Art Theatre, 1904), a three-dimensional box set gives the illusion of a real room. The actors act as if unaware of the audience, separated by an invisible "fourth wall", defined by the proscenium arch. The proscenium arch of the theater in the Auditorium Building, Chicago. It is the frame decorated with square tiles that form the vertical rectangle separating the stage (mostly behind the lowered curtain) from the auditorium (the area with seats).

The fourth wall is a common convention in narrative drama in which a metaphorical, invisible, or imaginary wall separates performers (actors, dancers, singers, etc.) from the audience, so that the audience sees through this "wall" into the performed narrative, but the performers behave as if they cannot see the audience in turn. The metaphor has also been extended outside of the theater, for instance to the typical boundary between character and audience in films, videos, or television programs, in which characters behave as if they are unaware of the camera. From the 16th century onward, the rise of illusionism in staging practices—culminating in the realism and naturalism of the theatre of the 19th century—led to the development of the fourth wall concept.