When was the Great Wall of China built?

The Great Wall of China is not a single wall but a series of fortifications built and rebuilt over roughly two thousand years. The earliest walls were constructed by rival states as early as the 7th century BC. After China was unified, the first emperor, Qin Shi Huang, connected and extended these walls in the 3rd century BC to defend against northern nomadic invaders. Successive dynasties continued to build and repair walls, but the grand stone-and-brick sections that most visitors see today were largely built during the Ming dynasty, from the late 14th to the 17th century. Altogether, the various walls stretch an estimated 21,000 kilometres. Contrary to a popular myth, the wall is not visible to the naked eye from space.