WE UNDERSTAND WHY - TO KEEP RAIDERS AND ENEMIES OUT, but to understand the enormous task of building it, staggers the mind.
Several walls were being built as early as the 7th century BC. Especially famous is the wall built in 220–206 BC by Qin Shi Huang, the first Emperor of China.
The Great Wall has been rebuilt, maintained, and enhanced over various dynasties; the majority of the existing wall is from the Ming Dynasty (1368–1644).
A comprehensive archaeological survey, using advanced technologies, has concluded that the walls built by the Ming dynasty measure 8,850 km (5,500 mi). This is made up of 6,259 km (3,889 mi) sections of actual wall, 359 km (223 mi) of trenches and 2,232 km (1,387 mi) of natural defensive barriers such as hills and rivers.
What an accomplishment !!