In imperial times, Gansu was an important strategic outpost and communications link for the Chinese empire, as the Hexi corridor runs along the "neck" of the province. The Han dynasty extended the Great Wall across this corridor, also building the strategic Yumenguan (Jade Gate Pass, near Dunhuang) and Yangguan fort towns along it. Remains of the wall and the towns can be found there to this date. The Ming dynasty also built the Jiayuguan outpost in Gansu. To the west of Yumenguan and the Qilian Mountains, at the northwestern end of the province, the Yuezhi, Wusun, and other nomadic tribes dwelt, occasionally figuring in regional imperial Chinese geopolitics. After the fall of the Uyghur Empire, a Uyghur state was established in Gansu that lasted from 848 to 1036 AD. During that time, many of Gansu's residents converted to Islam.