The earthwork forts that crown many hills in southern England are among the largest and most dramatic of the prehistoric features that still survive in our modern rural landscape. These defended enclosures, occupied from the end of the Bronze Age to the last few centuries before the Roman conquest, have long attracted archaeological interest and their function remains central to study of the Iron Age. The communal effort and high degree of social organisation indicated by hillforts feed debate about whether they were strongholds of Celtic chiefs, communal centres of population or temporary refuges occupied seasonally or in times of unrest. Yet few have been extensively examined archaeologically. Using non-invasive methods, the survey enabled more elaborate distinctions to be made between different classes of hillforts than has hitherto been possible. The new data reveals not only the complexity of the archaeological record preserved inside hillforts, but also great variation in complexity among sites. Survey of the surrounding countryside also revealed hillforts to be part of their contemporary landscape rather than isolated features.