Luxembourg is the capital and the largest city of Luxembourg. In the Middle Ages the Franks established a castle on the two rivers Alzette and Petrusse from which the Luxembourg is later developed. This area was of the great military significance at that time, so many fortresses were built. All these fortresses, the king´s palace, the cathedral from the 17th century are nowadays beautiful historical monuments worth visiting. Today Luxembourg is banking and administrative center, the seat of several institutions of the European Union. It has population of approximately 90 000.