When spectators arrive at a theater for a performance, they immediately take in the environment in which the event will occur. The atmosphere of the theater building has a great deal to do with the audience's mood in approaching a performance, not only creating expectations about the event, but conditioning the experience once it gets under way. A consideration of environment leads directly to an examination of the various forms and styles of theater buildings, including the arrangement of audience seating. Throughout theater history, there have been four basic types of stages, each with its own advantages and disadvantages, each suited to certain types of plays, and each providing the audience with a somewhat different viewing experience. The four are (1) the proscenium, or picture-frame, stage; (2) the arena, or circle, stage; (3) the thrust stage with three-quarter seating; and (4) created and found stage spaces. Today, in addition, there are all-purpose or "black box" theater spaces.