The earliest archaeological evidences were of the Majiabang and of the Hemudu cultures. The later Liangzhu culture, from around 2600–2000 BC, created complex and beautiful jade artifacts. Their economy was based on rice cultivation, fishing and constructed houses on stilts over rivers or lakes. During the Zhou dynasty, the Wu and Baiyue peoples inhabited the area with heavy aquaculture and stilt houses, but became increasingly sinicized through contact with northern Chinese states. They adopted the Chinese writing system and created excellent bronze swords. The Chu state from the west (in Hubei) expanded into this area and defeated the Yue state. After Chu was conquered by the Qin state, China was unified. It was not until the fall of the Western Jin dynasty during the early 4th century AD that northern Chinese moved to Jiangnan in significant numbers. The Yellow River valley was becoming barren due to flooding (lack of trees after intensive logging to create farmland) and constant harassment and invasion by the Wu Hu nomads.