The Great Wall of China
Great Wall of China, a fortified barrier built along the northern borders of ancient China. The wall was erected to bar marauding Huns and Tatars. It is constructed largely of earth and stone, with brick facing. Much of the Great Wall has weathered and crumbled, but substantial parts remain intact. It begins near the Yellow Sea northeast of Beijing and winds over hills and through valleys into the Alashan Desert in northwestern China. The Great Wall is about 1,500 miles (2,400 km) long. It varies in height from 15 to 30 feet (4.5 to 9 m). The top, along which a roadway runs, is about 12 feet (3.7 m) wide. Guard towers 40 feet (12 m) high stand about 200 yards (180 m) apart.
The Great Wall was begun during the third century B.C., when separate sections were built by various small kingdoms. After China was unified under the Chin dynasty in 221 B.C., the sections were connected into one continuous structure. During later dynasties, the Great Wall often lapsed into disrepair, but it was restored several times. The most significant restoration occurred under the Ming dynasty (1368–1644 A.D.); much of the present wall dates back to that era. After years of neglect, the Chinese government in 1979 established a commission to preserve the Great Wall as a national monument. Under its direction, many sections were rebuilt.