Northern France's main sights span thousands of years of history, from the awesome megaliths of Carnac, through the 18th -century grander of Nancy's town architecture, to Strasbourg's futuristic palais de I'Eropa, seat of the country's greatest cathedrals, such as those of  Reims  and Rouen. The region's most famaous religious monument is mont -St-Michel, whose evocative silhouette has welcomed