Yanmen Pass
In 202BC, the former peasant Liu Bang emerged victorious from the Chu–Han Contention that followed the rebellion that toppled the Qin dynasty, and proclaimed himself Emperor of the Han dynasty, becoming known as Emperor Gaozu of Han (r.202–195BC) to posterity. Unable to address the problem of the resurgent Xiongnu in the Ordos region through military means, Emperor Gaozu was forced to appease the Xiongnu. In exchange for peace, the Han offered tributes along with princesses to marry off to the Xiongnu chiefs. These diplomatic marriages would become known as "heqin", and the terms specified that the Great Wall (determined to be either the Warring States period Qin state wall or a short stretch of wall south of Yanmen Pass) was to serve as the line across which neither party would venture. In 162BC, Gaozu's son Emperor Wen clarified the agreement, suggesting the Xiongnu "chanyu" held authority north of the Wall and the Han emperor held authority south of it. Sima Qian, the author of the "Records of the Grand Historian", describes the result of this agreement as one of peace and friendship: "from the chanyu downwards, all the Xiongnu grew friendly with the Han, coming and going along the Long Wall". However, Chinese records show that the Xiongnu often did not respect the agreement, as the Xiongnu cavalry numbering up to 100,000 made several intrusions into Han territory despite the intermarriage.