It's a thousand times longer than any monument ever built. Started before the Birth of Christ, it was still being built when Columbus sailed to America and millions died in its making. What unspeakable fears drove the Chinese to build the Great Wall, a wall they called “the longest cemetery in the world”.

This is the wall that everybody knows about, where American presidents pose and millions of tourists visit every year. But few of those visitors realize that the floor they are rapidly wearing away and the walls they carve their initials on is younger than they are, rebuilt only a few decades ago.

But there is a lost wall, rarely visited and seldom filmed that lies just over the horizon. This is the real Great Wall of China. It starts on the shores of the Yellow Sea, and stretches through the mountains north of Beijing and into the heartland of North China. It has great fortified castles and watchtowers at crucial mountain passes where enemy armies could easily breach the defenses.

It runs down to the shoreline of great rivers, then for thousands of miles it stretches through uninhabited deserts across unscalable mountains. At first, it is built of stone, but as it reaches the desert, it reverses into mud brick. And finally, the Great Wall ends here at this lonely watchtower overlooking the White River. It's the greatest feat of engineering in the world, running a staggering total of more than 4,000 miles from start to finish.

This is the 15th dawn Chen Daling has photographed in this month alone. But Chen is not only a photographer. He is a man who has dedicated his life to discovering everything he can about the Great Wall of China. For years, he searched the Chinese countryside for evidence of long forgotten and abandoned walls.

breach: break through, burst into

unscalable: not possible to scale