Discussions of prehispanic warfare entail treatment of the relationship between ritual and war, and inform on interpretations of indigenous fortifications. Ten radiocarbon dates from recent excavations at the fortress of Acaray in the Huaura Valley, Peru, confirm the site was used during two periods: the Early Horizon (ca. 900–200 BC) and the Late Intermediate Period (ca. AD 1000–1470). These two periods are characterized by the construction of fortifications in neighboring valleys on the north coast and in the central highlands. The 23‐ha site of Acaray is one of the largest fortified sites known in the near‐north‐coast area, and it holds significant potential for exploring these two widely separated periods of conflict on the coast of Peru. This paper presents spatial and material data in light of the new radiocarbon dates. Site function during the two occupations is considered given our state of knowledge of regional dynamics and new excavations at Acaray. The early and late fortresses were built in re...