The Great Wall is primarily associated with China.
It is a vast system of fortifications built, rebuilt and expanded by successive Chinese states and dynasties over many centuries. The earliest walls date to periods before the Qin dynasty, while many of the best-preserved sections were constructed or strengthened during the Ming dynasty between the 14th and 17th centuries.
The wall’s purposes included border defence, troop movement, surveillance and control of trade routes. It is not one uninterrupted structure: the system includes walls, trenches, passes, watchtowers and natural barriers spread across northern China.
A popular myth says the Great Wall is visible from the Moon with the naked eye. It is not readily visible from the Moon, and even from low Earth orbit it is difficult to distinguish without aid. Its total measured length, including branches and associated features, is more than 21,000 kilometres.