Fortified defence system along the western border of the Chinese empire to protect it from Mongolian invasion., begun 4th century BC, completed 214 BC.
The oldest parts of the Great Wall (Chinese Wanli Changcheng or "10,000 Li Long Wall") date from the 4th century BC. Shih Huang-ti, the first emperor of the unified China, had the existing parts connected into one of the largest human constructions ever undertaken. The final wall and its branches run over a total distance of 6,758 km.
The work, completed in 214 BC, included watchtowers at regular intervals used to guard the wall and transmit messages through smoke signals during the day and fire signals during the night.
During later centuries the Great Wall fell into disrepair, but sections of it were repaired repeatedly. Several stretches of it are still well maintained and now attract large numbers of tourists.