The foundation of the Great Wall is made entirely of processed granites.  The quantity required was incredible.  However, granite is not always found along the route of the Great Wall.  Back then when productivity was low, the difficulties involved in the process of stone excavation and transportation are hardly imaginable to us today.  Yet, the Great Wall was completed.  But where were the granites excavated and processed?  This has been one of the greatest mysteries by which Great Wall experts are baffled.  We are standing at the remains of a granite processing ground.  Here, you can see processed and half-processed granites.  On one of the stones, visible markings signify that it is ready to be cut in halves.  In addition, a stone roller was found, which proves that explosives were used in the process of stone excavation.  The smooth stone cliff across is a cross-section left from stone excavation.  The discovery of this granite processing ground solved one of the mysteries of the Great Wall.