Meng Tian
During Qin dynasty, Shihuangdi sent Meng Tian, commanding 300,000 troops to defend his empire from Xiongnu's attacks. They spent 10 years connecting the Great Wall of Yan, Qin and Zhao, thus building Great Wall of Qin, the first Great Wall of 10,000 li, its 80-kilometer-long relics currently located in Batou (), or Erdaogou () in local slang, to the north of Zhangjiakou downtown area. The southern area of Zhangjiakou was under jurisdiction of Dai Commandery and Shanggu Commandery.