China is home to the Great Wall, a vast system of historic fortifications.
The Great Wall is not one continuous structure built at one time. It includes walls, trenches, passes, watchtowers, and other defensive works constructed and rebuilt across many centuries. Earlier walls existed before the Qin dynasty, and Qin Shi Huang connected sections after unifying China in the third century BCE.
Many of the best-preserved sections date from the Ming dynasty, which ruled from 1368 to 1644. The Ming built and strengthened walls to defend northern approaches, particularly against raids and incursions.
The wall’s total length is often given as more than 21,000 kilometres when all known sections and associated barriers are counted. The popular claim that it can be seen from the Moon with the unaided eye is false. Its main historical purpose was defence, border control, and communication.