Lay out a map of Britain and something odd becomes apparent: at 1 degree 50 minutes west there is a dead straight line going true north from Stonehenge to Lindisfarne. Two of Britain's most-ancient and most-revered sites. But there is more. Starting in the south, the line goes dead north from Castle Ditches to old Sarum, through Stonehenge, Knap Hill, and Avebury stone circles, past ancient places in Cricklade, Bibury, Notgrove, and Wootton Wawen. It goes through Long Low, Thor's Cave, Mam Tor, nearby Twelve Apostles stone circle, Ilkley Roman site, The Badger stone, ancient sites in Lanchester, Eochester, Millstone Burn, Bewick Hill and all the way to finish plum on Lindisfarne Island - one of the most ancient of early Christian sites and still a retreat and monastery. Robert Twigger has travelled this ancient line on foot, like a biologist walking a transect.