The Great Wall of China is not one wall but many. Far from being a single project it was the consolidation by the Ming dynasty of walls built locally to protect against the fierce northern tribes. Just one look shouted out the impossibility of assault on the wall at least by any civilisation not possessing helicopters. No one would be able to get around, under or over it at any point, both because of the solid severity of the structure and the lay of the landscape.
Yet there were arrow ports in both sides of the wall. If the northern tribes would be unable to reach the south side of the wall, what would be the need for arrow ports in the defences on that side? So in the name of defence, the Great Wall was in fact a spinal fortress, defensible against the assaults of hostile mobs of both the unenfranchised and the disenfranchised. Some things last centuries, it seems, even approaches to government.