It was built over a long period of time.
http://www.history.com/topics/great-wall-of-china
Who built the Great Wall of China?
I think a Qin emperor
3 answers
The history of the Great Wall of China began when fortifications built by various states during the Spring and Autumn (771–476 BCE) and the Warring States periods (475–221 BCE) were connected by the first emperor of China, Qin Shi Huang, to protect his newly founded Qin dynasty (221–206 BCE) against incursions by nomads ...
Ms. Sue is correct. It was nowhere near completion within Qin Shi Huang's lifetime. It was certainly a long-term project.