The great wall of China is an ancient fortificacionchina built and rebuilt between the 5th century BC and the 16th century to protect the northern border of the Chinese Empire during the successive dynasties of Imperial attacks of the nomadic xiongnu of Mongolia and Manchuria.
Counting its ramifications and secondary buildings, estimated that it has 8.851,8 km long, from the border with Korea on the verge of the Yalu River to the Gobi desert along an arc that outlines approximately south of Mongolia Interior rim, although today only 30% of it is retained. On average, measuring 6 to 7 meters tall and 4-5 meters wide. In its heyday, Ming, it was guarded by more than one million warriors.
The wall was named world heritage by Unesco in 1987. Much of the great wall is reputed to be the largest cemetery in the world. About 10 million workers died during the construction, but he was not buried them in the wall itself, but in its vicinity.
July 7, 2007 it became known that the wall of china was elected as one of the winners on the list of the seven wonders of the modern world.
The materials used for its construction were those available in different areas. Beijing nearby was limestone. Granite or fired brick was used in other sites. It was basically a long wall of clay and sand, covered with several brick walls. That made it highly resistant to impacts of siege weapons.
From the year 1938 it has been publishing in some books that the wall is visible from space. In fact, the great wall has only few meters from bandwidth - an approximate size of the slopes of highways and airports - and is almost the same color that the soil surrounding it, so it really is not possible such visibility. Thus statements of the astronauts who have treated during their spaceflight confirm it to discover it.