Great Wall of China… Ladders weren invented yet?
The wall was more than just the building. It was a part of a whole defensive system. In its main phase under the Ming Dynasty when the wall as we now think of it was built , there were small groups of soldiers posted well in front of of it linked by beacons and flags. If they saw invaders, they would signal back to soldiers staioned on the wall, who in turn would signal to the main body of troops stationed in barracks behind the wall. They would then advance through the wall and attack potential invaders. When the Ming Dynasty collapsed at a time of civil war the Manchus were able to gain access to the Chinese heartland when a general opened the gates and aloowed Manchu troops through.
