The first time I looked for the wall, I couldn’t find it. I had heard comparisons with the Great Wall of China, and had assumed that I would be able to see it from fifty miles away, maybe more. I had imagined there would be concrete fortresses all along its length, which was already 600 miles across the Sahara desert. It was said that more of the wall was being built all the time. No one knew how long it would finally be.

The idea was inconceivable: a wall built to protect the territory of Western Sahara that Morocco had occupied since 1975. It was the invention of Morocco’s King Hassan: what better way to keep out Polisario’s guerrilla army? It was the Hadrian’s Wall of North Africa, with 120,000 troops stationed on it. I imagined that it would rise sheer out of the desert.

In the event, it was quite different.