If you want to understand why the euro is in such trouble forget, for a moment, debt and sovereign bonds – and take a look at the bank notes. The images on euro notes are of imaginary buildings. While national currencies typically feature real people and places – George Washington on the dollar bill, the Bolshoi theatre on the Russian rouble – European identity is too fragile for that. Selecting a place or a hero associated with one country would have been too controversial. So the European authorities chose vague images that represented everywhere and nowhere.

Now, a decade after euro notes first emerged from cash machines across the continent, this lack of a common identity is the fatal flaw that may sink the common currency.

Over the weekend Tim Geithner, the US Treasury secretary, displayed palpable impatience with what the Americans see as a lack of political leadership in Europe. But the problem that is bedevilling the currency is not ultimately to do with leadership. It is more fundamental than that. The fact that national loyalties are much stronger than any common European loyalty means leaders are constrained in the solutions they can feasibly consider.