The only appliances for changing scenery that are mentioned by the ancient Greek writers are the ‘periaktoi’.[607] These were huge triangular prisms, revolving on a socket at the base. Each of the three sides of the prism consisted of a large flat surface, shaped like an upright parallelogram. One of these prisms was placed at each end of the stage, in such a manner as to fit in exactly with the scene at the back, and continue it in the direction of the side-wings. Each of the three sides was painted to represent a different view, but care was taken that in every case the painting should coincide exactly with the painting in the back-scene.[608] As the periaktos was turned round, it presented a different surface to the spectators. Accordingly it was possible, by revolving both the periaktoi, to make a change in the character of the scenery at each end of the stage, while the scene in the background remained the same as before. The periaktos to the right of the audience depicted views in the immediate neighbourhood of the city where the action was taking place. The periaktos to the left represented a more remote country. This fact corresponds exactly with the regulation already referred to, that the entrances to the right of the audience were reserved for people from the immediate neighbourhood, while people from a distance came in by the left. The principal use of the periaktoi must have been to produce a change of scene in cases where the prominent feature of the background remained the same. For instance, if the action had been taking place in front of a temple or palace, and was to be transferred to a temple or palace in a different country, the requisite alteration might easily be carried out by means of the periaktoi. The building in the background would remain the same, but the scenery on each side would be altered. Occasions for using the periaktoi might sometimes occur during the course of a single play. But such cases, as we have seen, were extremely rare. It must have been chiefly in the intervals between successive plays that the periaktoi were employed. Most Greek tragedies and comedies took place before a temple, a palace, or a private house. If therefore a series of plays was being exhibited, it might be convenient to retain the same scene in the background, and produce the necessary distinction between the different plays by altering the scenery at each side. The usage of the periaktoi was regulated by a curious conventional custom. If only one periaktos was turned round, the alteration in the scenery was, of course, confined to one end of the stage. This was done when the change of scene was supposed to be a slight one, and was merely from one part of the same district to another. But when the action was transferred to an entirely new district, then both the periaktoi were turned round, and the scenery was changed at each end. The representation of scenery on the periaktoi was probably