It took less than 10 minutes. At 9.30am on Sunday, four men arrived in a truck outside the Louvre in Paris, driving right up under a balcony and setting up a ladder with a furniture hoist. Two of them casually climbed up to the balcony and cut through the reinforced glass of a window; on the other side of the glass was the Apollo gallery, the most ornate and arguably the most beautiful room in the museum, Helen Pidd hears.