 Yanmen Commandery was first established around 300 during China's Warring States Period by the state of Zhao's King Yong, posthumously known as the Wuling ("Martial-&-Numinous") King.It covered territory in what is now northern Shanxi and southern Inner Mongolia.He created Yanmen Commandery along with its companion commanderies of Dai and Yunzhong to consolidate his conquests from invasions of the Loufan (t s "Lóufán") and "forest nomads" or "barbarians" ( "Línhú") in 306 and 304.