If the scene represented a dwelling-house, there were windows in the upper story, out of which the characters could peer upon the stage. Such windows are mentioned by Vitruvius, and instances of their use occur in the extant comedies. For example, Philocleon, in the Wasps, tries to escape out of an upper window, and in the Ecclesiazusae the old woman and the young girl are seen looking out of one.[589] It need hardly be remarked that the doors of the building represented by the painted scenery would correspond more or less closely with the permanent doors in the back-wall, so as to admit of easy ingress and egress to the actors. In the same way, if the scene was a cavern in a country region, the entrance to the cavern would be made to correspond with the central door in the wall at the back. Concerning the manner in which the scenery was finished off at the top nothing can be laid down for certain. It is not even known whether the stage was covered with a roof or not. But the analogy of Roman theatres, and the general convenience of the arrangement, are in favour of such a covering.[590] § 3. _The Entrances to the Stage._ The question as to the number and the character of the entrances leading upon the stage is of some importance in connexion with the Greek drama. In order to avoid confusion in dealing with this subject, it is necessary to distinguish carefully between the permanent doors in the walls surrounding the stage, and the temporary doors or entrances which were left when the scenery had been put up. First, as to the permanent doors. We have shown already that the remains of the purely Greek theatres are so defective, that it is impossible, from the evidence which they supply, to come to any conclusion as to the number of these doors. But it is evident, from the statements of Pollux, that the Hellenistic type of theatre, which is the one he describes, must have possessed at least five such doors. It must have had three doors in the wall at the back of the stage, and two doors at the sides, one leading from each of the wings. Probably the same plan was adopted in the older buildings of the fourth and fifth centuries, whether of stone or wood. In later times, when the Graeco-Roman theatres were erected, the stage was considerably lengthened, and in consequence the number of the doors in the wall at the back was raised to five. But it has been pointed out in the last chapter that in all probability only three of these doors were used in the course of the actual performances, and that the two outer ones were either covered over by the scenery, or concealed by temporary side-wings of wood.[591]