Great Wall

Great Wall, fortification along the northern and north-western frontier of China, running from Jinwangdao (Chinwangtao) on the Gulf of Chihli (Bo Hai or Po Hai) on the east to the vicinity of Gaodai (Kaotai), Gansu (Kansu) Province, on the west, with an inner wall running southward from the vicinity of Beijing almost to Handan (Hantan). The largest portion of the wall was erected by Shi Huangdi, first emperor of the Qin dynasty, as a defence against raids by nomadic peoples from the northern steppes. Systematic work on the wall was begun about 221 bc, after Shi Huangdi had united China under his rule, and it was finished about 204 bc. Small sections of the wall were probably already in existence, but Shi Huangdi is supposed to have had some 1,900 km (nearly 1,200 mi) of the wall erected during his reign. Speculation continues, however, as to whether the early “wall” was ever a single uniform fortification. In succeeding centuries, chiefly during the period of the Ming dynasty (ad 1368-1644), the Great Wall was repaired and extended, with masonry replacing the earlier earthworks. The fortification finally reached a length of about 2,400 km (about 1,500 mi), following the course of rivers instead of bridging them and conforming to the contours of the mountains and valleys in its path. The wall is built of earth and stone, faced with brick in the eastern parts. It is from 4.6 to 9.1 m (15 to 30 ft) thick at the base (about 6 m/20 ft on average) and tapers to some 3.7 m (12 ft) at the top. The height averages 7.6 m (25 ft) exclusive of the crenellated parapets. Watchtowers about 12 m (40 ft) in height are placed at intervals of approximately 180 m (approximately 200 yd). Several hundred kilometres of the Great Wall remain intact in the eastern reaches. It is reportedly the only man-made structure visible from space. Despite its size, it was never a secure defence against the nomad threat, which was only ended by the steppe campaigns of the Qing emperors, themselves the descendants of northern invaders. The Great Wall was designated a UNESCO World Heritage Site in 1987.