China is home to the ancient defensive system known as the Great Wall of China. Rather than one continuous wall, it is a network of walls, fortifications, trenches, and natural barriers built and rebuilt over many centuries.
The earliest sections were constructed by states before China was unified. Qin Shi Huang, the first emperor of a unified China, connected earlier walls in the third century BCE. The best-preserved sections visible today were largely built or strengthened during the Ming dynasty, from the 14th to the 17th centuries.
The wall's total measured length, including branches and associated features, is more than 21,000 kilometres. It was designed primarily for border defence and control, not as an impenetrable barrier. A popular claim says the Great Wall is visible from the Moon with the naked eye, but that claim is false.