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The Great Wall of China
The wall's construction began during the Warring States Period (403 to 221 BC). Shi Huangdi, first emperor of the Qin 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. This is the Qin Dynasty Wall.
After three years of civil war in 206 BC the first Han Dynasty was formed under the Gao Di Emperor, Liu Bang. After the Han army attacked and forced invaders from the North back across their northern borders, the Wall was extended to mark out new extended borders. This is the Han Dynasty Wall. In many areas the old Qin wall was simply restored. The extension, to build walls in the desert of the west, new methods of construction had to be devised. Here the soil consists of a gravel of sand and small stones. They used alternating layers of red willows and the gravel and lots of tamping. This produced a wall that has survived for some 2,000 years.
China would wait another 1,300 years before embarking on its greatest period of wall building. The Ming Dynasty built much of what remains today. The Ming Dynasty came into power in 1368 inheriting a nation crushed by 100 years of rule by the Mongols. The mighty Genghis Khan had united these tribes in 1206 and had pushed their way through China. A peasant revolt spelled the defeat of the Mongol empire. The leader of this revolt was Zhu Yangzhong who was installed as the first Ming Emperor. The Mings were to build the ultimate defense and lock the northern frontier once and for all. The Ming renovated the old Qin and Han walls and extended them. The Ming wall stretched some 4,500 miles from the Korean border at Dandong to the city of Jayuguan in the western desert. and I really doubt you can see it from space.
Shown here are views of the Ming Dynasty wall, from three sections: Badaling, Mutianya and Simatia
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