English: Chu-yen belonged to Chang-yeh, one of four commanderies west of the Yellow River established by Emperor Wu of the Han in the northwest frontier. In order to consolidate the northwest frontier defence, paupers and criminals east of the Han Ku Pass were sent to the frontier. Men from all over the empire also took turns as frontier garrison soldiers. A large number of these men settled there permanently. Han Chinese came into close contact with the Ch'iang, the Hsiung-nu, and various other people in the regions west of Tun-huang; hence, records excavated at Chu-yen contain considerable information regarding the non-Chinese who lived in the region.