This is a study of the Iron Age hillforts of north Ceredigion (Cardiganshire), mid Wales. Over one hundred diverse and unusual hillforts and defended enclosures are known in this topographically distinctive landscape, framed between the west coast of Cardigan Bay and the eastern high ground of the Cambrian Mountains. This new research sheds light on their architecture, chronology and the dynamic use of the regional terrain in later prehistory, reaching conclusions that have resonance for the wider study of British hillforts. The core of the study is a detailed analysis of the architecture of the later prehistoric hillforts of mid Wales, focusing on north Ceredigion. This shows them to have been sophisticated three dimensional spaces, built within a set of regional architectural traditions far more complex than has previously been acknowledged. In turn, these reflect the development of strong regional identities in later prehistory. This study also examines wider landscape themes including a model for overland 'cultural contact' linking mid Wales with other regions of the Severn and Wye valleys and western Britain, fossilised in the spread of distinctive shared ideas of hillfort design and construction.