Periaktos (plural form Periaktoi, from Greek revolving) is a device used for displaying and rapidly changing theatre scenes. It was first mentioned in Vitruvius' book on architecture, De architectura (c. 14 BC). It consists of a revolving solid isosceles triangular prism made of wood. On each of its three faces, a different scene is painted, so that, by revolving quickly the periaktos, another face can appear to the audience.