The Great Wall of China is one of the most famous historical megastructures and the world's longest structure created by man, even bigger than the pyramids and other colossal constructions. Despite a popular claim to the contrary, it is not visible from the Moon, although it is barely visible from near earth orbit.
A UNESCO World Heritage Site, the Great Wall of China is a protected space that has gained even more fame over the past decade because of international efforts to preserve sections that are falling into disrepair. Vandalism is one of the reasons the wall has suffered enormously over the past two decades. Local sellers often pick it apart to sell the parts to tourists.
The Great Wall of China was started inn the 5th century BC by the Qin Dynasty to protect the kingdom from attacks by the Xiongnu people. However, by the time construction started, there were already numerous towers and fortifications already standing. The construction of the wall was meant to join the different forts into one long structure and it took centuries to complete. Started, stopped, demolished, and rebuilt along the way, the Great Wall of China as it stands today was finished in the 16th century.
The structure is 4,000 miles (6,400 km) long and up to 26 feet (8 meters) in height. It has many watchtowers and towers along its length. The most popular sections with tourists are the ones near Beijing, especially Juyongguan pass and the Mutianyu Great Wall. The Shanhaiguan Great Wall, built as a bridge, is another popular stop for tourists walking along the wall. Most of it is constructed of bricks, although early parts are made of stones, earth, and tiles. To modern visitors, it looks remarkably similar along its length, but this is mostly due to the effect of wind erosion on the surface of the wall.