For 250 years, the cryptic inscription has exercised the minds of Britain's finest theologians, historians and scientists, including Charles Darwin, Josiah Wedgwood and, most recently, the Second World War code-breakers of Bletchley Park.
But an anonymous American researcher was credited yesterday with the best stab yet at what the letters D.O.U.O.S.V.A.V.V.M. - carved on the Shepherd's Monument at Lord Lichfield's Shugborough estate in Staffordshire - might actually signify.
The answer appears to be "Jesus (As Deity) Defy" - a message left by an 18th century Christian sect Priory of Sion, which was forced to keep its views secret since the Church of England thought they were heretical. On first impressions, this rather perplexing answer may disappoint those who believed the letters pointed the way to the final destination of the Holy Grail, the cup Jesus is said to have used during the Last Supper. But Shugborough Hall was holding on to its hopes last night, since the Priory of Sion was the spiritual successor to the Knights Templar, who were known as the keepers of the Holy Grail.
The stone monument, built around 1748, contains a carved relief of Nicholas Poussin's Les Bergers d'Arcadie II in reverse. Beneath it are the letters. The researcher, who applied standard codebreaking methods, initially came up with the message "Jesus H Defy" but says the H stands for Christ, hence the translation into "as deity". This is said to give the message a meaning of defiance against prevailing Christian norms.
This theory is given weight by the common belief that Poussin was a Grand Master of the Knights Templar. Its provenance is unexpected since Shugborough had drafted in veteran codebreakers of Bletchley Park to crack the code six months ago. But the publicity appears to have tantalised codebreakers from around the world, who came up with ideas connected to numerology, UFOs, secret messages to lost lovers and even Nostradamus.
Richard Kemp, the general manager of Shugborough, was convinced that the new theory provided another link to the Holy Grail. The previous connection was through Poussin's painting, which showed the Anson family who once owned Shugborough were interested in the Holy Grail by virtue of the painter's apparent Knights Templar affiliations.
Oliver and Sheila Lawn, who were code breakers during the Second World War, had qualified praise for the "Jesus H Defy" theory. Mr Lawn said he was "not sure" whether it was conclusive. "The person who propounded this ... has done a more thorough job than most of the others," he said. "He's made guesses but he's followed up the [historical] consequences more thoroughly." Mrs Lawn, meanwhile, has a more romantic interpretation, considering it to be a tribute by a lovelorn widower to his wife and her sister.