A periaktos (plural form periaktoi, from a Greek word meaning revolving) is a device used for displaying and rapidly changing theatre scenes. It was first mentioned in Plato's Republic, in the story, "Allegory of a Cave" (c. 375 BCE), but its most intense use began in Renaissance theatre, as a result of the work of important theatrical designers, such as Nicola Sabbatini (1574–1654). It consists of a revolving solid equilateral triangular prism made of wood. On each of its three faces, a different scene is painted, so that, by quickly revolving the periaktos, another face can appear to the audience. Other solid polygons can be used, such as cubes, but triangular prisms offer the best combination of simplicity, speed and number of scenes per device.