The origin of the Great Wall is the intersection of the two.

After Qin Shihuang destroyed the Six Kingdoms, in order to recover lost territory, he sent general Meng Tian to lead 300,000 troops to crusade against the Huns and drive them to the north of the Yellow River. In order to set up a county in the north and defend the frontier, Qin Shihuang began to build the Great Wall on a large scale. In 2 14 BC, Qin Shihuang connected the Great Wall of the vassal States of Yan, Zhao and Wei, which lasted for more than 10 years. It took 300,000 people to build it continuously, and completed Lintao (Min County) in Gansu Province in the west, along the Yellow River to He Lin in Inner Mongolia, Yinshan in the north, Yanmenguan, Daixian and Yuxian in Shaanxi Province in the south, and the Great Wall of Yan State in the north.