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Top 10 Feats of Engineering
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No. 10 - Great Wall of China

At first glance, the Great Wall doesn't seem so amazingly difficult to build - I mean, it's just a big stone wall, right?

But take a step back to grasp its length and you might get a different perspective. Stretching 4,000 miles across China, the wall is actually a series of several walls that were built, rebuilt, merged and expanded over the course of 2,000 years, which certainly makes it the lengthiest undertaking of any engineering project.

While the first versions of the wall were built as early as 400 B.C., the version of the wall that we see today dates back only as far as the A.D. 15th to 17th centuries.

And by the way, it's not all that visible from space.

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