Book excerpt: Who built the megaliths, those massive stone structures ranging from tombs to standing stones that date back to over 4000 BC? Why were they built? How were the enormous stones transported and erected? Were these strange, sacred stones used as temples or tombs, sculptures or houses? Covering the best-known sites - Avebury and Stonehenge in England, Carnac in France and Knowth in Ireland - and also less famous examples in Scandinavia, Malta, Egypt and Spain, this book considers the special significance - architectural, scientific, religious and cultural - of these enigmatic Neolithic stone structures.