From Cornwall to Orkney, prehistoric stone circles are scattered throughout the length and breadth of the British Isles. Their history stretches more than 2 millennia, during which time their use by prehistoric cultures changed dramatically. They are fascinating examples of how a monument's purpose can evolve overtime. Their remains continue to attract great amounts of visitors right up to the present day. To learn more about these extraordinary prehistoric structures, I'm chatting with Timothy Darvill OBE, a professor from the Department of Archaeology and Anthropology at Bournemouth University and the author of Prehistoric Britain.