Why the mighty Stonehenge was built around 5,000 years ago has long been one of the great mysteries.But according to a new study, we may finally have an answer.Scientists say Wiltshire's famous stone circle was built as a symbol of unification between three distinct corners of Britain.We know that Stonehenge's rocky slabs were transported as far afield from southwest Wales and northeast Scotland.So the scientists, from University College London and Aberystwyth University, theorise that Scottish and Welsh people brought their own local stones down to Wiltshire as a well-meaning contribution to assembling the structure.In that sense, it represented a powerful...