Answer:
The history of the Great Wall of China began when fortifications built by various states during the Spring and Autumn and Warring States periods were connected by the first emperor of China, Qin Shi Huang, to protect his newly founded Qin dynasty against incursions by nomads from Inner Asia.
The total length of all sections of the Great Wall of China ever built adds up to about 21,196 kilometers (13,171 miles), including overlapping sections that were rebuilt. The wall constructed during the Ming dynasty, the most well-preserved section, is about 8,850 kilometers (5,499 miles) long.