(1928) A collaborative adaptation of an English piece called "The Beggar's Opera", by John Gay. The Threepenny Opera revolutionized theater by breaking what is known as the "fourth wall". The fourth wall is the imaginary barrier between two universes: that of the stage and that of the audience. The wall is an artificial division that was thought to allow audiences to detach themselves from the material being presented on stage. Breaching the fourth wall, a tactic termed "the alienation effect", was devised by Bertolt Brecht. Brecht intended to force audience members to an awareness of the world of the play (and, by extension the greater structure of society as a whole) as an artificial construct. Weill and Brecht collaborated with Elisabeth Hauptman on this anti-capitalist piece. The Threepenny Opera is the source of the song "Mack the Knife", later covered by Ella Fitzgerald, Frank Sinatra, Louis Armstrong, Bobby Darin, and more.