As far as the current administrative divisions are concerned, the sixteen states of Youyun probably include the whole territory of Beijing and Tianjin, as well as Hebei and northern Shanxi. In ancient times, these places were divided into sixteen states: Yan (right), Ji, Ying, Mo, Zhuo, Tan, Shun, Yun, Confucianism, Gui, Wu, Xin, Wei, Ying, Huan, Shuo and * * *. Among them, You, Ji, Ying, Mo, Zhuo, Tan and Shun are located in the southeast of the northern branch of Taihang Mountain, and the rest of Yun, Confucianism, Gui, Wu, Xin, Wei, Ying, Huan and Shuojiuzhou are located in the northwest of Shanxi.

What is so special about this place? First of all, from a macro geographical point of view, this place is actually the "border between Han and Hu", and there is a very important dividing line in China's geography: the 400 mm isobath line is relatively dry to the north, and the ancient mode of production is mainly nomadic; On the other hand, to the south, it is the traditional land of China dominated by farming civilization. And this line generally coincides with the Great Wall.