My summer riverboat cruise from Amsterdam to Budapest along the Rhine, Main and Danube proved to be fully as instructive as it was relaxing. The majestic hilltop fortresses, castles and palatial edifices, erected to keep out tribal hordes, also testify to indulgences pursued by monarchs, princes and bishops over hundreds of years of relentless self-aggrandisement that left state coffers bare, subjects in poverty and rulers reduced to the status of robber barons.