Daixian County, Shanxi Province
The great wall of China is not one wall but many — physical walls, yes, but also a set of fortified passes that controlled movement between the steppe and the sown. The most important of these passes, by any historical measure, is Yanmen Pass. For more than 3,000 years, this cleft in the Gouzhu Mountains — at the northern edge of Daixian County, under Xinzhou Prefecture — was the primary military gateway between the Central Plains and the Mongolian plateau.…