File photo shows workers working in a salt refinery in Ningchang ancient town of Wuxi, Southwest China's Chongqing municipality. The history of local salt production here can be traced back to over 4,000 years ago according to historical records. Brine pits in Wuxi served as a key source of salt production in the Three Gorges area. The ancient salt-trading road, which started from east Sichuan, now east Chongqing, and ran through China's hinterland, served as an important carrier of economic and cultural exchanges in the joining regions of Hubei, Chongqing, Hunan and Guizhou in the ancient times. [Photo/Xinhua]