The Great Wall of China is a fortification along the northern and north-western frontier of China. 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, between about 221 BC and 204 BC. Small sections of the wall were probably already in existence, but Shi Huangdi is supposed to have had nearly 1,200 miles of the wall erected during his reign.
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 1,500 miles, 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 15 to 30 ft thick at the base (about 20 ft on the average) and tapers to some 12 ft at the top. The height averages 25 ft exclusive of the crenellated parapets. Watchtowers about 40 ft in height are placed at intervals of approximately 200 yds. Several hundred miles 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.
Historical information is from "Great Wall," Microsoft(R) Encarta(R) 98 Encyclopedia. (c) 1993-1997 Microsoft Corporation. All rights reserved.
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