Great Wall of China,fortifications,c.1,500 mi (2,400 km) long,winding across N China from Gansu prov.to Hebei prov.on the Yellow Sea.The wall,running mostly along the southern edge of the Mongolian plain,was erected to protect China from northern nomads.It is an amalgamation of many walls built in ancient times; the first unified wall was built in the 3d cent.B.C.by the Ch'in dynasty.Laborers were conscripted from all over China to build it,and many of them died during the project.The wall's present form dates substantially from the Ming dynasty (1368–1644).It averages 25 ft (7.6 m) in height and is 15 to 30 ft (4.6–9.1 m) thick at the base,sloping to 12 ft (3.7 m) at the top.Guard stations and watchtowers are placed at regular intervals.The eastern part of the wall is earth and stone faced with brick,but in the west it is merely an earth mound.Successive invasions of China from the north demonstrated that the Great Wall had little military utility.Since 1949 two sections N of Beijing have been reconstructed and are open to visitors.
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