became a national anthem. Das Rheingold – inspired by the Nibelungenlied, the Rhine is one of the settings for the first opera of Richard Wagner's Der Ring des Nibelungen. The action of the epic opens and ends underneath the Rhine, where three Rheinmaidens swim and protect a hoard of gold. The Loreley/Lorelei is a rock on the eastern bank of the Rhine, that is associated with several legendary tales, poems and songs. The river spot has a reputation for being a challenge for inexperienced navigators. At the end of World War I, the Rhineland was subject to the Treaty of Versailles. This decreed that it would be occupied by the allies, until 1935 and after that, it would be a demilitarized zone, with the German army forbidden to enter. The Treaty of Versailles and this particular provision, in general, caused much resentment in Germany and is often cited as helping Adolf Hitler's rise to power. The allies left the Rhineland, in 1930 and the German army re-occupied it in 1936, which was enormously popular in Germany. Although the allies could probably have prevented the reoccupation, Britain and France were not inclined to do so, a feature of their policy of appeasement to Hitler. In World War II, it was recognized that the Rhine would present a formidable natural obstacle to the invasion of Germany, by the Western Allies. The Rhine bridge at Arnhem, immortalized in the book, A Bridge Too Far and the film, was a central focus of the battle for Arnhem, during the failed Operation Market Garden of September 1944. The bridges at Nijmegen, over the Waal distributary of the Rhine, were also an objective of Operation Market Garden. In a separate operation, the Ludendorff Bridge, crossing the Rhine at Remagen, became famous, when U.S. forces were able to capture it intact – much to their own surprise – after the Germans failed to demolish it. This also became the subject of a film, The Bridge at Remagen. Seven Days to the River Rhine was a Warsaw Pact war plan for an invasion of Western Europe during the Cold War. Until 1932 the generally accepted length of the Rhine was . In 1932 the German encyclopedia Knaurs Lexikon stated the length as , presumably a typographical error. After this number was placed into the authoritative Brockhaus Enzyklopädie, it became generally accepted and found its way into numerous textbooks