With longer daylight, we look forward to a warmer and beautiful summer when we (hopefully) can once again go on a city trip. Our guest today is Hilbert de Wal, city guide and cultural expert with via-cultura.nl. The common theme today are the historic places that commemorate Carolus Magnus or Charles the Great or Charlemagne, the 'founder' of Europe. The springs and the Dom in Aachen, the unspoilt industrial heritage of Liege, fortifications and cathedrals in Maastricht. Why was Aachen in the early medieval far more important as a city than Maastricht or Liege with their strategic location on the river? What was Charlemagne's greatest innovation? He is seen as the inventor of education.