Often, the only clue he has, is from some ancient text. And it is up to him to puzzle out the arcane references and make them fit the modern landscape.

Armed only with a walking stick to fend off snakes and rabid dogs, he has walked many thousands of miles, but he has had many successes. After struggling up this forested mountainside, he discovered a long-lost wall. No one had ever noticed it before but once it was part of an ancient Great Wall, too much earlier, and in a completely different location from the wall everyone knows. And the more scientists and archeologists probe, the more mysterious it all becomes. In a lifetime of searching, Chen has discovered thousands of miles of forgotten walls. In fact, if you add up all the walls that we now know about, it comes to a staggering total of 35, 000 miles, almost enough to stretch around the planet twice. But why built so many walls at such an enormous cost? What were the Chinese afraid of?

It was said you could smell them coming, even before you heard the thunder of their hooves. Then they were on you, slaughtering, raping, pillaging and burning. Behind them, they left a trail of smoking cities and bleached bones. They were the nomadic hordes of the northern plains, the Huns, Mongols, Manchus, all at war with the settled life of the Chinese.

The Chinese were terrified by the nomads and detested their harsh way of life. A famous poem said they have no fields or pastures, only wastes where white bones lie among yellow sands. Nomads live solely off their livestock. Their animals provided every basic need: food, milk, meat, hides for clothes and the yurt - the nomadic tent. Animal dung provided fuel. In this uncompromising landscape, it was the only way to fuel a fire. The harsh climate kept the nomads always on the move, looking for pastures suitable for their flocks. When disease and freezing weather decimated their animals, the nomadic hordes raided the Chinese when they refused to trade with them. China had everything the nomads didn't have, rice, silk, writing and a very elaborate civilization. The Great Wall was a barrier between the civilized world of the Chinese and barbarians.

arcane: secret, hidden; mysterious; occult

forested: covered with trees, thickly wooded

yurt: rounded building characteristic of the Mongols and the Turks of central Asia

dung: animal excrement