One of the most famous structures in the world can be found to the northwest and north of Beijing, China. Said to be visible from the moon, the Great Wall is the longest fortified line ever built. It zigzags to the east and west along the mountains, stretching more than 1,500 miles.
Construction of the Great Wall began in the 7th century B.C. It stands about 25 feet high and has 40-foot towers built into it every 200 to 300 yards. The wall tapers from a 25-foot base to about 15 feet at the top. Its sides are made of earth, brick and stone, while the top is paved with bricks set in lime, forming a roadway for horsemen. The Great Wall was built entirely by hand and took hundreds of years to complete.
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