Six centuries and no one can read it

At Yale's Beinecke Library sits a manuscript of some 240 pages that nobody has ever managed to read. It's known as the Voynich manuscript, after the book dealer who bought it in 1912, and carbon dating places its parchment in the early fifteenth century.

It is written in an alphabet that appears in no other known document, and illustrated with plants matching no real species, astronomical diagrams, and women bathing in strange green tubs.

The finest minds have tried: cryptographers who cracked military codes in the world wars, linguists, mathematicians and, more recently, artificial intelligence. No one has produced an accepted translation. It isn't even clear whether it's a real language, a cipher, or a very expensive joke.

Six centuries on, it remains exactly this: the only book in the world that has defeated every single one of its readers.