In London, the Elgin Marbles were hidden in Aldwych tube station – although, alarmingly, it was later revealed it wouldn’t have withstood a direct hit. In Paris, the Louvre was emptied out in 1939, with 3,600 paintings packed off to safe houses. The Mona Lisa – now considered too fragile to be moved – was shuttled round the country five times, moving from chateau to abbey to chateau, to keep her one step ahead of the Nazis.