Almost every stage production uses a pulley system or some sort of rope system to suspend something. Whether it be a curtain, backdrop, or even an actor, using counter weights to hold something up is an old practice. Ropes are all brought down from the ceiling to a row along the wall, over pulleys. These ropes have a plate with vertical pipes on the bottom, and the weights rest on top of the plate. The other end is attached to a horizontal bar on the stage, which multiple things can be attached to. If the weight equals the weight of the bar and what it's carrying, then the pulley system won't move. The weights won't ever be exact, so a brake system to lock the ropes in place is used to ensure that the bar is held in place.