Quick answer for how long did it take to build the Great Wall of China: No exact completion date, continuous build for over 2000 years.
The Great Wall of China had been a continued project for over 2000 years. It took 9 years between 221 BC – 206 BC under the first emperor of China, Qin Shi Huanghe for the first section of the wall to be completed. The wall had been continually built and rebuilt over centuries and the majority of the current Great Wall of China was completed between 1368 and 1644 AD during the Ming dynasty.