Two interesting passages from Designing and Making Stage Scenery by Michael Ware:
"The historian Pollux, writing in the second century AD, tells us of some of the machinery used in the Greek theatres. He mentions trap-doors, hoists, cranes, lightning and thunder machines, devices for revealing dead bodies – rolled or swung out on what today we would call 'trucks' or 'wagons'. He also describe the Piraktoi which were revolving prisms painted differently on each facet, and the Mechane for lowering a god at the appropriate moment. Whether all these devices were used by the Greeks in the fifth century BC is doubtful, though we do know that dead bodies had to be revealed mechanically as slaughter was not allowed on the stage; and we know that Euripides lowered the occasional god from above to round off the action of the play."
"In Italy and France the enthusiasm for the theatre of illusion and of spectacle had led to a diminished interest in the drama and an increase of interest in the proliferation of design for opera and ballet. Architects began to specialise in designing scenery. It was very profitable. Vast opera houses were being constructed by princes all over Europe to keep up with the other princes. It is an arguable point whether the building of opera houses is more conducive to the harmony of humanity than the making of nuclear bombs, but in the seventeenth century rivalry was confined the explosion of new scenic devices. Giacomo Torelli was the first artist to specialise in designing scenery; some of his effects were so astute that it was rumoured in Venice that he was in league with the devil, which shows the power of the dedicated designer."