The Great Wall of China is actually not just one wall, but a series of walls built in Northern China to protect against intruders. The total length of the wall, including trenches and other natural barriers, is 5500 miles. Construction started in 5th century BC with stamped earth and wooden board frames. Although some parts of the wall have been renovated (including sections in Beijing that host many tourists) many other parts are disappearing due to erosion.
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