It is a series of fortifications made of wood, bricks, stones and other materials, The wall was built in 220-206BC by 1st emperor China Qin Shihuang, Great Wall of China measure 8,850KM, 359 km of trenches and 2,232 km of natural defensive barriers like Rivers and Hills, Other survey found that Wall with its all branches measure 21,196KM, the Chinese are already famous some techniques of wall building by the 5th and 8th Centuries BC.
Great Wall of China Mainly made with rammed earth, wood, stones and then Bricks, Bricks are mostly used in many areas of wall and other materials Such as tiles and lime and defensive gaps are 30CM tall and 23M wide for guards could survey the surrounding area, Signal towers are built on tops of hills and other high points for their visibility, Gates are mostly made with wood and could be used for traps against those going through Barracks, stables and armories are built to near surface of inner wall.
If we talk about wall’s condition then some portions of north Beijing near to tourists center is preserved and renovated and in some locations Wall is disrepair, Some Parts of wall has been destroyed for other constructions, Around 60KM of wall may be disappear in next 25 years because of erosion from sandstorms and this area is in Gansu province, In some places the height of wall has been reduced more than 5Meter to less than 2Meter.
The square lookout towers most famous images of the Great Wall of China has been completely disappeared, In Aug 2012 30Meters area of wall in Hebei province north China collapsed after continuous heavy Rain.
In 1754 an English antiquary William Stukeley wrote (This mighty wall of four score miles in length is only exceeded by the Chinese Wall, It makes a considerable figure upon the terrestrial globe, and may be discerned at the Moon). In Oct 2003 an astronaut Yang Liwei who belongs to china said he had not been able to see the Great Wall of China, A Chinese American astronaut Leroy Chiao took a photo from International Space Station that shows the Great Wall of China.