Mystery manufacturing processes - GIFs

[IAMSatisfied]

As the camera pans over the wall, stop the video at about the 8 second mark and you'll notice cross-hatch marks engraved in the nearer stones... which leads me to believe they might be grain grinding stones. You can also see in the wall construction that these discs are of varying thicknesses... some have no hole, some one and others two. In the pile to the left of the wall you'll see stone cylinders, which may have been used to grind grain in this manner:



Here's another photo that may indicate surplus/worn/defective wheels are in abundance in China: