It's one of the longest and largest structures ever built and it was designed to defend one of the oldest and greatest civilizations on the planet

And for centuries it did just that and for some centuries it didn't do that at all

Some people have claimed that you can see it from space and it's one of the

most visited tourist attractions on Earth. Learn more about the Great Wall of

China, one of the planet's greatest man-made wonders on this episode of Everything Everywhere Daily. To understand why the Great Wall of China was built you first have to understand the geography of China.

The historic center of China and of Chinese civilization has been in what is today the eastern third of China.

This region of China has had the vast majority of the

population for all of its history. And this region is relatively flat and

extremely fertile. The agricultural production of this region is why China has historically had such high populations and a high population density.

Even thousands of years ago when populations on Earth were much lower, China still usually had the highest population in the world

because this region was so productive.

China has often been divided by an imaginary line called the Hu Line.

It stretches from the city of Ha'heihue in the north near the border of Russia

to Tengchong in the south which is close to the border of Myanmar. The western side of this line

has about two-thirds of the land of modern-day China, but only 6% of the population.

The eastern side of the line has 94% of the population and almost all the agriculture.

The eastern side of that line is what the defense of China has always been about.

Now consider how China has historically viewed its defenses. To the east you have the Pacific Ocean.

The only real island off the coast of China is Taiwan, which traditionally never has really been that populated.

Japan is further to the north and lies across the sea from Korea and Siberia.

The Philippines is further south, but it lies across the sea from Korea and Siberia. The Philippines is further south

but it lies across the sea from Southeast Asia. So the coast of China has never

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