Baoji it has a population of 3,670,000 according to the 2001 Chinese census, making it the 25th largest city in China, and a surface area of 18172 km². The city itself has a population of approximately 800,000. Surrounded on three sides by hills, Baoji is in a valley opening out to the east. Its location is strategic, controlling a pass on the Qinling Mountains between the Wei Valley and the upper Han River,or named Chia-ling River,(嘉陵江,Chia-ling Chiang,Jialing Jiang)]. Passing through Baoji is the ancient North Silk Road, the northernmost route of about 2600 kilometres in length, which connected the ancient Chinese capital of Xian to the West over the Wushao Ling Pass to Wuwei and emerging in Kashgar before linking to ancient Parthia.