Another theory of a far more revolutionary kind has been propounded in recent years by Höpken[459], and amplified and developed by Dörpfeld. Dörpfeld assumes, like Wieseler, that the proscenium of the fifth century must have been of the same height as that described by Vitruvius. But he gets out of the consequent difficulty by supposing that the proscenium was intended, not as a stage for the actors, but as a background. He denies the existence of a stage in purely Greek theatres either of the earlier or of the later period. He believes that in all Greek theatres the actors and the chorus performed together in the orchestra. The proscenium represented the palace or other building before which the action took place. The front-wall of the stage-buildings immediately behind the proscenium represented merely the sky. This theory has been the subject of much discussion and controversy during the last twenty years. As it has been accepted by several scholars, it will be necessary to consider it in detail. I propose in the present section to explain the grounds on which, as it seems to me, it must be regarded as untenable; and to discuss at length the evidence on which the belief in the existence of a Greek stage is founded. In dealing with this subject it will be convenient to divide the period covered by the Greek drama into two parts, and to consider first the later part, from about 300 B.C. onwards; and then to return to the earlier period, that of the fourth and fifth centuries. The evidence in the two cases is somewhat different, and will be more clearly understood if taken separately.