There at Piantou Pass ( t , s , Piāntóuguān) in Xinzhou, Shanxi province, the Great Wall splits in two with the "Outer Great Wall" ( t , s , Wài Chǎngchéng) extending along the Inner Mongolia border with Shanxi into Hebei province, and the "inner Great Wall" ( t , s , Nèi Chǎngchéng) running southeast from Piantou Pass for some 400 kilometers , passing through important passes like the Pingxing Pass and Yanmen Pass before joining the Outer Great Wall at Sihaiye ( , Sìhǎiyě), in Beijing's Yanqing County.