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Taken at face value, it is nothing more than a postcard of a religious painting, sent by a holidaymaker to one of his closest friends. The signature on the back, however, suggests that all might not be what it seems.
Sent by the legendary cryptologist Alan Turing to his psychologist Dr Franz Greenbaum, it appears to be a coded reference to one of history’s most enduring mathematical puzzles, as well as a possible hint to his thoughts of suicide.
The missive has been sold for £28,000 at auction, its high price reflecting the rarity of letters sent by Turing, after the auctioneers became convinced that it contained a hidden message.
Today, Turing - portrayed by Benedict Cumberbatch in the acclaimed 2014 film The Imitation Game - is lauded as a war hero who helped crack the Enigma code at Bletchley Park, Britain’s codebreaking centre, as well as being the father of artificial intelligence.
When the postcard was sent on July 23, 1953, however, he was an anonymous, tortured soul whose homosexuality had led to a criminal conviction and made him effectively unemployable.
He had tried to give himself a lift by staying at Club Mediterranee in Corfu, from where he wrote: “I hope you are all enjoying yourselves as well as I am here at Corfu. It is tremendously hot and one wears bathing things all day."
Rather than sending Manchester-based Dr Greenbaum and his two daughters a picture postcard of the beaches, Turing chose an image of the illuminated cover of Antiquities of the Jews by the historian Flavius Josephus.
As Turing undoubtedly knew, the First Century writer was the originator of the Josephus Problem, a mathematical puzzle otherwise known as the “suicide circle” or “Roman roulette”.
Fighting against the Romans in the First Jewish-Roman War, Josephus and 40 other soldiers became trapped in a cave in July 67AD, surrounded by the Roman forces. Refusing to surrender, the group decided suicide would be preferable, and Josephus suggested a unique method.
After drawing lots, they stood in a circle, and soldier No.1 killed the man to his left, the next man standing killed the man to his left, and so on, going around the circle as many times as it took for only one man to be left alive.
Josephus worked out where he would have to be standing at the beginning in order to be the only man left alive at the end, and betrayed his comrades by surrendering to the Romans when all the others were dead.
The theme of suicide was an appropriate one for the postcard, as Turing would take his own life using cyanide a year after he sent the postcard.
Robert Livingston, of the US-based RR Auction, said: “Turing, who was fascinated by these types of algorithmic puzzles, surely knew of the ‘Josephus Problem’ and it is likely the reason he chose this specific postcard.
“Connecting mathematics through the ages, this is a truly remarkable piece.”
Convicted of gross indecency in 1952 after admitting a homosexual relationship, he had agreed to undergo chemical castration as an alternative to a jail sentence. Dr Greenbaum noted that Turing became more and more mentally unstable as his “treatment” progressed, and Turing had complained to his friend that his house was being watched by the authorities, who regarded him as a security risk because of his compromised personal life.
His mother Sara Turing, who wrote a biography of her son, noted that he “normally shirked letter-writing”.
In 2009, the then Prime Minister Gordon Brown made a public apology on behalf of the British Government for the “appalling way he was treated”. He was granted a posthumous pardon by the Queen in 2013.