Which structure is the longest man-made monument in the world?

The Great Wall of China is the longest man-made monument in the world, with all sections and branches measured at about 21,196 kilometres. It is not one continuous wall built at one time, but a network of fortifications constructed and rebuilt across many centuries.

Early walls were built by separate Chinese states before the Qin dynasty unified major sections in the third century BCE. Later dynasties expanded or repaired the defenses, and many of the best-preserved brick and stone sections date from the Ming dynasty, which ruled from 1368 to 1644.

The wall’s purposes included border defense, troop movement, surveillance, communication, and control of trade routes. Towers and beacon systems allowed signals to travel over long distances.

A common misconception is that the Great Wall can be seen from the Moon with the unaided eye. It generally cannot. The wall is also not uniformly made of brick: materials included packed earth, wood, stone, and brick, depending on local resources and historical period.