The Stanley Kubrick exhibition at London’s Design Museum examines the making of every one of the extraordinary director’s films. But its opening section is devoted to a film he didn’t make: a biopic of Napoleon Bonaparte. As odd as that might seem, Kubrick fans are almost as fixated on Napoleon – to use its working title – as they are on anything else in his awe-inspiring canon. Critics regularly hail it as the greatest and most tantalising unfinished film of all. Besides, the story of how Napoleon was nearly-but-not-quite made exemplifies Kubrick’s sky-high ambition, his ravenous intellectual curiosity and his obsessive planning. “We put the display upfront because it’s a beautiful illustration of his process,” says Adrienne Groen, the co-curator of the Design Museum’s exhibition. “You can see his methods, and the amount of material he gathered before he even started.”

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This material consists of photographs, sketches, and documents, among them a gracious letter from Audrey Hepburn, turning down the role of Napoleon’s wife Joséphine de Beauharnais. (David Hemmings was the writer-director’s choice for the lead role.) There is a selection of Kubrick’s 276 books about the French emperor, including Felix Markham’s biography, which is illuminated with asterisks, underlinings and notes: “Who assassinated Tsar Paul? How did the politics really work?” Most intriguing of all is a wooden cabinet of index cards which Groen’s co-curator, Deyan Sudjic, calls “an analogue Wikipedia”. Pick any day in Napoleon’s life, pull open the appropriate drawer, flick to the corresponding index card, and there is information covering everything, says Sudjic, “from what he had for breakfast to what Josephine was wearing at dinner”.