The site of Xuanquan Posthouse refers to the remains of an important courier station in the Hosi Corridor built in the Han Dynasty during 2nd century BC and 3rd Century AD, located in the Gobi desert to the north of Huoyan Hill, which is an offshoot of Qilian mountains. The heritage has a complete structure, and a large number of Chinese documents written in bamboo and wooden slips from Han Dynasty were unearthed there, recording the postal system in the large transportation system of the Han Empire. These documents witnessed how the Xuanquan Posthouse guaranteed the transportation and communication along the Silk Roads.
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See more - http://www.silkroads.org.cn/article_1122_1.html