A Proscenium theater is a theater space whose primary feature is a large archway (the proscenium arch) at or near the front of the stage, through which the auience views the play. The audience directly faces the stage, which is typically raised several feet above front row audience level. The main stage is the space behind the proscenium arch, often marked by a curtain which can be lowered or drawn closed. The space in front of the curtain is called the "apron." The areas obscured by the proscenium arch and any curtains serving the same purpose (often called legs or tormentors) are called the wings. Any space not viewable to the audiences is collectively referred to as offstage. Proscenium stages range in size from small enclosures to several stories tall. In general practice, a theater space is referred to as a "proscenium" any time the audience directly faces the stage, with no audience on any other side, even if there is not a formal proscenium arch over the stage. Because of the somewhat incongruous nature of a theater called a proscenium theater without a proscenium arch, these theatres are often referred to as "end-on" theater spaces.