LONDON–“Some frontiers are only in the imagination” wrote Jan Morris in her “Fifty Years of Europe”. Prince Metternich used to say the frontier of Asia was at the Landstrasse, the street which ran towards Hungary away from Vienna’s city walls. It is also said that Konrad Adenauer, the first chancellor of West Germany after World War 2, held similar feelings about Prussia. He was a Rhinelander, and whenever his train crossed the Elbe, on its way eastward to Berlin, he too would groan, “Hier beginnt Asia”, and pull the blinds down. After last week-end’s momentous event, the launching of the single currency, the Europeans now have to consider where they go next. Do they in fact need frontiers within Europe any more? If they can come this far, shouldn’t they let their imaginations work further and complete the journey to a United States of Europe? By any measure of history...