AS A BUILDING, Rosslyn Chapel, on the outskirts of Edinburgh, is intriguing. The exterior features Gothic gargoyles and flying buttresses, while inside there are ornate pillars, carvings and an extraordinary ceiling. As a place of mystery, it is a magnet for those with exotic - some might say outlandish - theories. Built in the mid-15th century by some of the best stonemasons in Europe, the chiselled scenes and symbols would have been easily understood by their medieval audience but seem baffling to us today. The most striking example of their craft is the Apprentice Pillar, which is beautifully carved and...