Side pieces or ‘wings’ on either side of a perspective drawing enhance the depth effect, in the first example trees and a house, in the second example curtains. The winding road in the first example creates a connection between foreground and background.
Wings were often used in theatres in the past: on both sides of the stage were wooden props, painted with nature or architecture. The actors or dancers could enter and leave the stage from behind these side pieces.
The back wall of the stage was usually a large painted canvas. In the following image from the sixteenth century, such a perspective set is drawn. You can clearly see the thicknesses of the sturdy wooden wings, painted with mountains, clouds and the sea. On the floor of the stage are figures in a semi-circle. The second from the right is the Roman god of the sea Neptune with his trident. The backdrop is painted with clouds, the sea and a large ship. The horizon is approximately halfway along the backdrop.
EXTRA: Draw the bare construction of the set (so without the mountains, clouds, sea and human figures) or download/print this image and only trace the construction. Then create a different environment on the wings and the backdrop.