In this paper, we report 11 AMS radiocarbon dates from 8 Prehispanic fortifications located in the Huaura Valley, central coast of Perú. Small fragments of organic material embedded in preserved mud mortar in architecture, and samples from construction layers exposed by looter's holes were used to date architectural features without undertaking extensive excavations. These dates contribute toward refining the chronology of fort building in the valley, and provide a test for assumptions about temporal change and architectural style. The results indicate that fortifications date to at least 3 periods. These data provide a starting point for exploring the occurrence of warfare through time on a regional scale.