Mike Parker Pearson is Professor of British Later Prehistory at University College London. A distinguished prehistorian he has been involved with many major projects, including leading the recent Stonehenge Riverside Project. His many publications include Stonehenge: Exploring the Greatest Stone Age Mystery (2012) and From Machair to Mountains: archaeological survey and excavation in Uist (2012). Colin Richards is Professor of World Prehistory in the Deaprtment of Archaeology at the University of Manchester where he mainly specialises in Neolithic archaeology, architecture and monumentality and ethnoarchaeology, with specific interests in Orkney and Easter Island.