The Great Wall of China

The first major wall was built during the reign of Qin Shi Huangdi, the first emperor of China during the Qin (Ch'in) Dynasty (221 B.C - 206 B.C.).  It was created by joining several existing walls built previously by regional governments.  This first wall was built much further north than the current Great Wall, and made of materials that have largely dissappeared over time. 

The Great Wall that can still be seen today was built during the Ming Dynasty (1368-1644), on a much larger scale and made of stone on the sides and top.  The wall housed garrisons, signal fires, and a messenger and postal service.  The primary purpose was to make it difficult and slow for nomadic armies to get their horses across the wall.  Without their horses the Huns were not a serious military threat.    It is 4000 miles long, or 6400 km., and is visible from Earth orbit.

Comments

[Hakim]

The great wall is not visible from space. Length doesnt matters. Think about it, wouldnt we see asphalt highways then? Try to think about someone holding a string 1 mile away. No matter the length of string, you wont see it!

[Bob Shaver]

A Chinese astronaut said that he couldn't see the Great Wall from Earth orbit, but US astronaut Gene Cernan is quoted as saying that "At Earth orbit of 160km to 320km high, the Great Wall of China is indeed visible to the naked eye".

Cernan reckons Yang simply wasn't trying. He said: "If you know where to look and you look hard enough, you can also see the Astrodome in Houston, Texas, where I live."

The theory of the reader's comment is that the wall is only 30 feet wide or so, and no matter how long it is, you can't see an object only 30 feet wide. My theory is that when the sun is at the right angle, the shadow cast by the wall could be 1/4 mile wide, thus visible. Plus someone who has been there, Gene Cernan, confirms it. Now from high orbit or from the moon, maybe its not visible to the naked eye.

[michaela]

i think the great wall of china was the best idea in the world to stop the mongolions from attaking china and it also stops wars im michaela jeffrey and im only 13 my dad tells me about the great wall of china and i carnt believe it is 4ooo miles i so want to see china and i have 4 sisters and 1 brother and they are all older than me and i herd thet in china there are no brother or sisters or aunty or uncle and i heird if you have more than 1 child the child will be killed and the mother will be in jail so i hope ill get to see the great wall of china but i now it wont come true so thanks for reading and remamber im only 13 bye

[charity]

i always dream to travel on that great wall of china, i think its very interesting but im still young. That great wall of china was on our history subject when i was still in grade 4 and our teacher told us that it was a beautiful place to see.

[Beijing Dai]

Today, a visit to the Great Wall is fascinating and also a chance to do a bit of hiking in the mountains. Unmissable.