Which wall is the world’s longest man-made structure?

The Great Wall of China is the world’s longest man-made structure.

The Great Wall is a network of fortifications built and rebuilt across northern China over many centuries. Its total length, including trenches and natural barriers, was measured by a 2009 survey at about 8,850 kilometres. A broader archaeological survey later reported a total of roughly 21,196 kilometres when all known sections from different periods are included.

The best-preserved and most famous sections date from the Ming dynasty, which ruled from 1368 to 1644. The wall helped control movement, protect agricultural regions, and support border defence, although it was not an impenetrable barrier.

The popular claim that the wall is visible from the Moon is false. Even from low Earth orbit, it is difficult to see with the unaided eye because its materials and colour often blend with the surrounding landscape.