History, legend and memory have long pointed to Co Loa, an earthwork enclosure outside Hanoi, as the seat of an indigenous power that gave identity to the people of the Bac Bo region, north Vietnam. Survey, excavation and a set of radiocarbon dates now put this site on the historical map. The main rampart of the middle circuit was built in the later centuries BC, before the coming of Han Imperial China. Nor was this rampart the first defence. The authors show the potential of archaeology for revealing the creation and development of a polity among the prosperous people of...