China is home to the Great Wall, the ancient defensive fortification.
The Great Wall is not one continuous structure built at one time. It is a network of walls, fortifications, trenches, and natural barriers constructed and rebuilt by different Chinese states and dynasties over many centuries.
The Qin dynasty connected earlier walls in the third century BCE, while the Ming dynasty built or restored many of the stone and brick sections most visited today. The entire defensive system, including associated features, extends for more than 20,000 kilometres.
A common misconception is that the Great Wall is clearly visible from the Moon; it is not visible to the unaided eye from there. Its main historical purpose was border defense and control of movement.