A lot of people assume we've excavated the entire site and everything we've ever going to know about the monument is known," said historian Susan Greaney of English Heritage. " but actually, there's quite a lot we still don't know and there's quite a lot that can be discovered just through non- excavation methods. That stil leaves the mystery of what happened to the missing stones. Were they used tobuild houses or roads in the area? No one knoes,but english heritage may purposely avoid watering some areas of Stonehenge during the next dry spell to see if the answers to other puzzles emerge