The Great Wall of China is a series of fortifications made of stone,brick,tamped earth,wood,and other materials,generally built along an east-to-west line across the historical northern borders of China to protect the Chinese states and empires against the raids and invasions of the various nomadic groups of the Eurasian Steppe.
Other purposes of the Great Wall have included border controls,allowing the imposition of duties on goods transported along the Silk Road.
While some portions north of Beijing and near tourist centers have been preserved and even extensively renovated,in many locations the Wall is in disrepair.
On April 18 in 2009,the length of the Wall was announced after a full investigation.it is 5500 miles.
The Great Wall of China cannot be seen from space,In October 2003,Chinese astronaut Yang Liwei stated that he had not been able to see the Great Wall of China.
