The Helan Mountains of western China long divided the land of nomads from the land of settled farmers. The passes through the mountains were gateways between different civilizations. One of those passes, Helankou Gorge, has long been famous for its astonishing array of rock art.
Some petroyglyphs are scattered all along the gorge, but at its eastern end is a dense mass of more than 5,000 carvings.
These are now a Chinese state park, and a World Museum of Rock Art has been built nearby.
Another theory is that this is a sacred way or pilgrimage route, one taken over by Buddhists and maintained. The continuity certainly speaks to the spiritual power of the landscape. (The peculiar image above is called by Chinese archaeologists the "sun god.")