给定一个英语问题，生成一个回答该问题的段落。


"What is the history behind the Great Wall of China?"
The Great Wall of China is a series of fortifications built by various Chinese dynasties over centuries spanning from the 7th century BC to the Ming dynasty in the 17th century AD. Its construction was motivated by the need to protect Chinese states and empires against raids and invasions by various nomadic groups from the North such as the Mongols and Manchus. The wall measures over 13,000 miles in length and remains an iconic symbol of Chinese civilization and military might.