The wall's construction began during the Warring States Period (403 to 221 BC). The Great Wall is a fortification along the northern and northwestern frontier of China, running from Shanhaiguan on the Gulf of Bohai on the east to the vicinity of Gaodai, Gansu Province, on the west, with an inner wall running southward from the vicinity of Beijing almost to Handan. Shi Huangdi, first emperor of the Chin dynasty erected the largest portion of the wall as a defense against raids by nomadic peoples. 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 nearly 1,200 miles of the wall erected during his reign.

300,000 men --- many of them political prisoners whose bodies are rumored to be buried in the wall (not actually true) --- were put to work connecting the segments into one huge rampart of stone and earth. In succeeding centuries, chiefly during the period of the Ming dynasty (AD 1368-1644), the Great Wall was repaired and extended by reinforcing it with cement and stone. 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 feet thick at the base (about 20 feet on the average) and tapers to some 12 feet at the top. The height averages 25 feet exclusive of the crenellated parapets. Watchtowers about 40 feet in height are placed at intervals of approximately 200 yards. Several hundred kilometers of the Great Wall remain intact in the eastern reaches.

The amount of brick and stone employed to construct the Great Wall could circumscribe the earth with a dike eight feet high. From the 6th to the 14th centuries, the wall ceased to be an effective barrier against determined invaders, who discovered that bribing the sentries was their most effective weapon. The Chinese Emperors helped in this cause by failing to pay their army troops, generally a bad mistake. If you don't pay your army, someone else will.