Here I am on the Great Wall of China, also known to the Chinese as the '10,000 Li Wall' (5000 km), is about 70 kilometers from Beijing and is at an elevation of about a 1000 meters.
This section of the wall was restored in 1957. It stretches from the
Shanhaiguan Pass on the east coast to Jiayuguan Pass in the Gobi Desert.
It was begun 2000 years ago during the Qin Dynasty (221-227 BCE) when China was united under Emperor Qin Shihuang. Note: he also had the stupendous (8000 plus) terra-cotta warriors and horses made for his burial site in Xi'an, standardized the currency and written script.
Separate walls were constructed by various independent kingdoms and then were joined to keep out invading marauding nomads. Hundreds of thousands of people, many political prisoner took ten years of hard labor to complete under the direction of General Meng Tian. An estimated 180 million cubic meters of rammed earth was used to form the core. The wall never did perform the function it was designed for.
Genghis Kan stated, "The strength of a wall depends on the courage of those who defend it". Since people could be bribed it didn't do much good as far as keeping out the nomads. As a matter of fact, some people think it kept the Chinese inside the country more than other people out. It could be used as a highway though and by using fires on the watch towers, messages could be passed back to the capital within a remarkably short time so it was good for something!
During the Ming Dynasty the wall was rehashed by facing it with bricks and stone slabs - some 60 million meters of them! The Ming project took 100 years to complete and caused hardship and many deaths just to appease an emperors desires.
The wall was largely forgotten after that and much has returned to dust. Most of the rest was carted off by peasants during the cultural revolution to construct houses and other buildings.
The wall probably would have disappeared if it hadn't been for the tourist industry. Several sections have been refaced and now instead of it being a symbol of tyranny, it is a symbol of beauty!