The authors present new research on the Chifeng area of north-eastern China where they have been studying the remains of a society of the second millennium BC. This northern region, which saw the introduction of agriculture at the same time as the Yellow River basin experienced a brief and intensive period of fortification in the Late Neolithic/Early Bronze Age: natural ridges above the valleys were ringed with double stone walls and semicircular towers enclosing clusters of round houses with yards. Using large-scale survey and analysis of the structures at the key site of Sanzuodian, they place this phenomenon in its cultural and social context.