I’m a mountain guy, I decided, after just a few hours in the outskirts of the Gobi desert. It was hot, and blowy, the Great Wall we were following was practically impossible to see, and the ground beneath us was parched and covered in huge salt pans. Give me a goat track, I thought. A ridge ripped by a cold wind from Siberia, and a Ming wall I can actually see. But my friend Chinoook is made of sterner stuff (though I give him a run for his money on my home turf). Out ahead, he led the way through the salt pans towards a brown smudge on the horizon. “There’s the wall”, he promised. I squinted. “Sure it is”, I thought skeptically. But he was right. Just meters off a salt pan they could have used as a set for Mordor in the Lord of the Rings, stood an enormous, multi-tiered wall – a giant layer cake two thousand years old.