The largest and most important of these movable decorations was the curtain (aulaeum) which served to conceal the stage from the public. The upper models shows the working quite well. During performances the curtain remained rolled up in al longitudinal channel at the top front of the stage area (pulpitum) and connected to the place from which the stagehands could operate the machinery that raised and lowered it.
This machinery consisted of a system of counterweights hanging from masts of up to four meters above the surface of the stage to which the curtain was fastened. In this theater archeologists have located ten curtain wells containing fragments of wood set into iron ferrules whcih protected the bases of the masts. Look at the picture below.
The mechanism fell into disuse after the reform of the Roman theater during the reign of Flavius. If you look at wooden stage at the picture in my message "Repeat:...", you can see the curtain wells.