In theatre, a platform (also referred to as a riser or rostrum) is a stationary, standard flat walking surface for actors to perform on. Typically, they are built to be assembled modularly. They are often used to provide varying levels, to make a show more visually interesting. They are also used to separate areas on stage, and as seating bleachers. This is in contrast to scenery wagons, which are mobile platforms that are supported by casters instead of feet.