The (re)occupation of hillforts was a distinctive feature of post-Roman Europe in the fifth to seventh centuries ad. In western and northern Britain, hillforts are interpreted as power centres associated with militarized elites, but research has paid less attention to their landscape context, hence we know little about the factors that influenced their siting and how this facilitated elite power. Geographic Information Systems (GIS) provide opportunities for landscape research, but are constrained by limitations of source data and the difficulty of defining appropriate parameters for analysis. This article presents a new methodology that combines data processing and analytical functions in GIS with techniques and principles drawn from ‘traditional’ landscape archaeology. A case study, focused on Dinas Powys, suggests that the strategic siting of this hillfort facilitated control over the landscape and has wider implications for our understanding of patterns of power in post-Roman Britain.