Qin Shi Huang conquered all opposing states and unified China in 221 BC, establishing the Qin Dynasty. His intention was to impose centralized rule and prevent the resurgence of feudal lords, he ordered the destruction of the wall sections that divided his empire along the former state borders.

To protect the empire against intrusions by the Xiongnu people from the north, he ordered the building of a new wall to connect the remaining fortifications along the empire's new northern frontier.

There are no surviving historical records indicating the exact length and course of the Qin Dynasty walls. Most of the ancient walls have eroded away over the centuries, and very few sections remain today.

It is estimated that over 1 million workers died building the wall.

Here is a video about the Great Wall of China, 长城 Cháng chéng=Great Wall