East of the Jiayuguan fort, there is a section of the Great Wall which is so steep that it is called the “Overhanging Great Wall” (or, as certain poorly-translated signs nearby say, the “Cantilevered Great Wall.”) The Chinese name is 悬臂长城 (Xuánbì chángchéng) and, yes, Beloved Reader, that is the same 悬 (xuán) in the name of the Hanging Temple. Well-spotted.
It was built when, in the eighteenth year of his rule, Emperor Jiajing of the Ming Dynasty ordered the strengthening of military defenses around the Jiayuguan area by the building of two sections of wall along the Heishan Gorge.
In the middle of the gorge is the Water Gate, straddling the river.
Westward, toward the fort, you can see the Great Wall continuing off over the hills.
I started the long walk to the top.
More of a hike than a walk, really.
It was a hard climb. I was sucking wind. I was starting to feel really awful about myself, but became slightly encouraged to see the Chinese Army using the wall as part of their physical regimen. I signed up for Chinese culture & history, not boot camp!
At the top, I looked back at the panorama of of the mountains with Jiayuguan City in the distance. 
If you were a foolhardy barbarian from the north, this is what you would have looked forward to if you decided to attack.
At the bottom of the climb down there were fake camels to remind everyone of how tightly bound together the Great Wall and the Silk Road are. 