The Great Wall

The  Great  Wall  of  China  is  the  largest  defence  fortification   and  the  greatest  building  enterprise    ever  undertaken   by   man.  About  1500  miles  long,  this  unique  wall  stretches  from  the  Gulf  of  the  Yellow  Sea  along  the  northern  frontier  of  China  to  Kansu Province in the west.  The  width of  this  wall varies  from  15 to 40 feet at  the  base,  and  from  12 to 35 feet at the summit. Its height ranges from 20 to 50 feet. It is the only structure on earth that can be identified from the moon.

Walled frontiers between the kingdoms in China date from at least the 4^th century BC. In the 3^rd century BC, the first emperor of “Ch’ in”, after uniting China, linked up the existing walls and built new sections to create the Great Wall as a continuous unit.

His purpose was to defend China from the Huns on the north. Watch towers and garrison stations were set at regular intervals in order to send signals and guard the bulwark. The wall was constructed in such a way that troops summoned by beacon fire could be quickly transported along its top.
The wall was built mostly of rubble, although the western sections are of tamped earth and important passes are of brick or masonry. The wall was frequently modified in later centuries. Some of its sections were built in the 15^th and 16^th centuries with new facilities of high towers. Before that, extensive repairs and extensions were made at various periods, notably during the Ming dynasty