China contains most of the Great Wall of China. The wall is a vast system of fortifications built and rebuilt across northern China over many centuries.
Although commonly described as a single wall, the Great Wall includes walls, trenches, watchtowers, fortresses, and natural barriers. Earlier defensive structures existed before the Qin dynasty, while the best-preserved sections were built during the Ming dynasty from the 14th to the 17th centuries.
The Ming walls were intended to protect agricultural and political centres from incursions by groups from the northern steppes. They were made from different materials depending on local resources, including tamped earth, brick, stone, and wood.
A popular myth says the Great Wall can be seen from the Moon with the unaided eye. Astronauts have generally explained that it is difficult or impossible to distinguish without optical aid because its materials resemble the surrounding landscape.