Introduction to Dongtianmen Pass: Dongtianmen Pass is the strategic point connecting Qin, Jin and Yanzhao. It is a double-pass city, divided into East Pavilion and West Pavilion. The two pavilions are less than 50 meters apart, dividing the east and west peaks of Baishi Ridge. , garrisoning troops and guarding them, relying on each other, and forming an integrated whole. There are two ruts under Guancheng that are 18 meters long and more than a foot deep at their deepest. The rock surface of this roadbed is obviously lower than both sides. This is the tunnel of the "Yan-Jin Thoroughfare".