From Wikipedia: Periaktos (plural form Periaktoi, from Greek revolving) is a device used for displaying and rapidly changing theatre scenes. It has been first mentioned in Vitruvius' book on architecture, De architectura (ca. 14 BC) but its most intense use began in the Renaissance theatre, as a result of the work of important theatrical designers, such as Nicola Sabbatini (1574-1654). 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.