On day five of my jeep journey along the Great Wall I reached Luowenyu, near Zunhua, Hebei Province.

I remembered this point in my journey, walking along the Wall in November 1987. My feet were frozen and had been for days. I was so tired I didn't even feel like taking photographs any more.

Even so, for some serendipitous reason, I decided to take a shot of a broken-down section of the Wall.

I did not know that 79 years before another foreigner had passed by. But three years later, after I published my adventures in Alone on the Great Wall, his book The Great Wall of China was sent to me.

William Geil was the first man to travel the length of the Wall and also the first to write a book dedicated to the subject.

He was also the first photographer to show the world what the Wall looked like far away from Beijing.

It was because we both, coincidentally, had taken pictures of the Wall from the same spot, 79 years apart, that I became acquainted with Geil.

Many Chinese people ask me if we are somehow related. They think I am a grandson following in my grandfather's footsteps - after all, we do share a Christian name.

I always say that our relationship is a bond forged by a mutual passion for the Wall and a mutual desire to see it from end to end.

If we had met, perhaps we would have introduced ourselves by saying, "Hello, I'm William and I'm walking the length of the Wall." It would have been like an echo.

Climbing Luowenyu I imagined my predecessor doing the same, with his 25-man entourage struggling behind him carrying wooden boxes, containing his camera, lenses and tripod.

I once again imagined two days - in 1908 and 1987 - when two different Williams took their photos and made their journeys along this immense monument.

Since 2003 I've traveled 35,000 km across China with my camera, tripod, and Geil's vintage photos, replicating his shots to create a record of the Wall's changes over the years.