The study traces the economic and demographic history of a corner of China's southeast coast from the third to the thirteenth centuries, looking at the relationship between changes in the agrarian and urban economies of the area and their connections to the expanding role of domestic and foreign trade. It provides a previously unexplored perspective on the role of commercialized production and trade in a regional economy in the premodern era and demonstrates that trade was able to drive change in a premodern economy in a way that has not generally been recognized.