Max Pearson

So we'd have to go down the mountains to collect water and then climb back up again, which took several hours and a lot of energy.

So we'd try to ration how much water we drank.

Back then, we didn't have the modern outdoor clothing and equipment that's available today.

We just had army uniforms donated to us by soldiers in a couple of army units we came across en route.

So when a rainstorm came over, we just get soaked.

And it rains a lot in the mountains.

Snow was also a problem.

We were walking in snow for months.

It's also pretty dangerous, especially when you are walking downhill.

Many of the little villages the team visited along the wall had developed because of the trading opportunities it had offered, and some of the locals were descendants of the people who actually built it.

The ancestors of one community we came across had been moved from the far south of China to help build the wall, and even now, 500 years on, they keep up their southern traditions, even though most of them have never ever been to the south.

Yao Huidong and his team took photographs and copious notes of what they saw on their travels, building up a comprehensive record of the wall mile after mile.

Basically, as they built the Great Wall, they used the natural terrain to their advantage whenever they could.

So they built fortifications where it was easy to defend and hard to attack.

They also used the material that was at hand.

So where stones are easy to come by, they use them like bricks.

Elsewhere in granite areas, they use the big boulders.

And on the plains, for example, they just use the compacted earth.

In strategically important areas, there will be more than one wall, sometimes two or three deep, a few kilometers apart, so that if the first wall fell, there were reinforcements behind it.

Communications in rural China in the 80s were minimal.