Great Wall
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Condition
While some portions near tourist centers have been preserved and even reconstructed, in many locations the Wall is in disrepair, serving as a playground for some villages and a source of stones to rebuild houses and roads. Sections of the Wall are also prone to graffiti and vandalism. Parts have been destroyed because the Wall is in the way of construction sites. Intact or repaired portions of the Wall near developed tourist areas are often plagued with hawkers of tourist kitsch. After one of the many runs for charity along the Great Wall, H.J.P Arnold questioned several runners about the status of the wall. A typical response was “The wall was clearly discernible and only moderately eroded along 22% of the run. The Wall was usually discernible but frequently broken/eroded 41% of the run, and scarcely discernible and almost totally eroded 37% of the run.”
Watchtowers and barracks
The wall is complemented by defensive fighting stations, to which wall defenders may retreat if overwhelmed. With more than 10,000 watch towers (which were used to store weapons, house troops, and send smoke signals), each tower has unique and restricted stairways and entries to confuse attackers. Barracks and administrative centers are located at larger intervals.
Communication between the army units along the length of the Great Wall, including the ability to call reinforcements and warn garrisons of enemy movements, was of high importance. Signal towers were built upon hill tops or other high points along the wall for their visibility.
Recognition
The Wall was made a UNESCO World Heritage Site in 1987.
Mao Zedong had a saying, “You're not a real man if you haven't climbed the Great Wall”. Originally this saying was used to bolster his revolution in trekking north. But due to erosion of time the saying has been reduced to a promotional slogan for the Great Wall of China. In Badaling (north of Beijing), the 'real man stone' can be found with the saying engraved in it.
From outer space
Richard Halliburton's 1938 book Second Book of Marvels said the Great Wall is the only man-made object visible from the moon, and a Ripley's Believe It or Not! cartoon from the same decade makes a similar claim. This belief has persisted, assuming urban legend status, sometimes even entering school textbooks. Arthur Waldron, author of the most authoritative history of the Great Wall, has speculated that the belief might go back to the fascination with the “canals” once believed to exist on Mars. (The logic was simple: If people on Earth can see the Martians' canals, the Martians might be able to see the Great Wall.)
In fact, the Great Wall is only a few meters wide - similar in size to highways and airport runways - and is about the same color as the soil surrounding it. It cannot be seen by the unaided eye from the distance of the moon, much less from Mars. If the Great Wall were visible from the moon, it would be easy to see from near-Earth orbit, but from near-Earth orbit it is barely visible, and only under nearly perfect conditions; it is no more conspicuous than many other manmade objects.
Astronaut William Pogue thought he had seen it from Skylab but discovered he was actually looking at the Grand Canal of China near Beijing. He spotted the Great Wall with binoculars, but said that “it wasn't visible to the unaided eye.” US Senator Jake Garn claimed to be able to see the Great Wall with the naked eye from a space shuttle orbit in the early 1980s, but his claim has been disputed by several US astronauts. Chinese astronaut Yang Liwei said he could not see it at all.
Veteran US astronaut Gene Cernan has stated: “At Earth orbit of 160 km to 320 km high, the Great Wall of China is, indeed, visible to the naked eye.” Ed Lu, Expedition 7 Science Officer aboard the International Space Station, adds that, “it's less visible than a lot of other objects. And you have to know where to look.”
Neil Armstrong stated about the view from Apollo 11: “I do not believe that, at least with my eyes, there would be any man-made object that I could see. I have not yet found somebody who has told me they've seen the Wall of China from Earth orbit. ... I've asked various people, particularly Shuttle guys, that have been many orbits around China in the daytime, and the ones I've talked to didn't see it.”
Leroy Chiao, a Chinese-American astronaut, took a photograph from the International Space Station that shows the wall. It was so indistinct that the photographer was not certain he had actually captured it. Based on the photograph, the state-run China Daily newspaper concluded that the Great Wall can be seen from space with the naked eye, under favorable viewing conditions, if one knows exactly where to look.
These inconsistent results suggest the visibility of the Great Wall depends greatly on the seeing conditions, and also the direction of the light (oblique lighting widens the shadow). Features on the moon that are dramatically visible at times can be undetectable at other times due to changes in lighting direction; the same would be true of the Great Wall.
Based on the optics of resolving power (distance versus the width of the iris: a few millimetres for the human eye, metres for large telescopes) an object of reasonable contrast to its surroundings some four thousand miles in diameter (such as the Australian land mass) would be visible to the unaided eye from the moon. But the Great Wall is of course not a disc but more like a thread, and a thread a foot long would not be visible from a hundred yards away, even though a human head is.
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