The principal aim of this short chapter is to present some ideas and suggest possible directions of research concerning the development of the north-western Portuguese Iron Age, and in particular its late—and most dynamic—phase, that which coincided with Roman acculturation and conquest, towards the end of the first century BC. These processes of acculturation and conquest, and their impact on the Iron Age communities of the region, have long been the subject of discussion and indeed misunderstanding. Many unresolved questions and contradictions have blurred the construction of a coherent picture which is only now starting to take shape, though not necessarily providing definitive answers. If there was an effective military conquest, where is the evidence for the destruction of sites in the archaeological record? If the northwest was already conquered and pacified, why were the local communities building and reinforcing defensive walls? If the Romans were controlling this region, why were hillforts still being built in the traditional indigenous fashion? Generations of archaeologists, myself included, have attempted to answer some of these questions in the course of our research. The Iron Age cultures of northwest Iberia are broadly characterized by hillfort settlements built in stone, either granite or schist. These hillforts, known locally as ‘castros’, provide the name by which the culture is generally known: ‘cultura castreja’, in Portugal, or ‘cultura castrexa’ in Galicia. The word ‘castro’ obviously derives from the Latin ‘castrum’, in the sense of defended settlement. Francisco Martins Sarmento introduced this terminology following his major excavation work at the Citânia de Briteiros, from the 1870s onwards. Martins Sarmento’s excavation and survey work, combined with his remarkable capacity for observation and analysis, brought the Castro culture to widespread international attention, particularly after the Ninth International Congress of Anthropology and Prehistoric Archaeology, held in Lisbon in 1890. Despite this promising start, the Castro culture remained little known to most European archaeologists until the last few decades of the twentieth century, save for the contribution made by Christopher Hawkes (1971; 1984).