For reasons of simple geography, travellers leaving or entering China to or from Central Asia and the West have always been channelled through the narrow strip of land that runs 1000km northwest of Lanzhou. With the foothills of the Tibetan plateau, in the form of the Qilian Shan range, soaring up to the south, and a merciless combination of waterless desert and mountain to the north, the road known as the Hexi Corridor offers the only feasible way through the physical obstacles that crowd in west of Lanzhou.
Historically, whoever controlled the corridor could operate a stranglehold on the fabulous riches of the Silk Road trade. Inevitably the Chinese took an interest from the earliest times, and a certain amount of Great Wall-building was already taking place along the Hexi Corridor under Emperor Qin Shi Huang in the third century BC. Subsequently, the powerful Han dynasty succeeded in incorporating the region into their empire, though the influence of central government remained far from constant for many centuries afterwards, as Tibetans, Uyghurs and then Mongols vied for control. Not until the Mongol conquests of the thirteenth century did the corridor finally become a settled part of the Chinese empire, with the Ming consolidating the old Great Wall positions and building its magnificent last fort at Jiayuguan.
Two other cities along the corridor, Wuwei and Zhangye, offer convenient places to break the long journey from Lanzhou to Dunhuang, and have their own share of historic sights. All three cities lie on the same train line and have regular services.