In November 1997 English Heritage announced the discovery of a vast prehistoric temple in Somerset.
The extraordinary wooden rings at Stanton Drew are the most recent and biggest of a series of remarkable discoveries that have transformed the way archaeologists think of the great monuments in the region, including Avebury and Stonehenge; one of the world's most famous prehistoric monuments, top tourist site and top location for summer solstice celebrations.
The results of these discoveries have not been published outside academic journals and no one has considered the wider implications of these finds.
Here Mike Pitts, who has worked as an archaeologist at Avebury, and has access to the unpublished English Heritage files, asks what sort of people designed and built these extraordinary neolithic structures - the biggest in Britain until the arrival of medieval cathedrals.
Using computer reconstructions he shows what they looked like and asks what they are for.
This is the story of the discovery of a lost civilisation that spanned five centuries, a civilisation that now lies mostly beneath the fields of Southern England.