The Shugborough Inscription is a sequence of letters – O U O S V A V V, between the letters D M – carved on the 18th-century Shepherd's Monument in the grounds of Shugborough Hall in Staffordshire, England, below a mirror image of Nicolas Poussin's painting, the Shepherds of Arcadia. It has never been satisfactorily explained, and has been called one of the world's top uncracked ciphertexts.
The monument was built sometime between 1748 and 1763, commissioned by Thomas Anson, paid for by his brother, Admiral George Anson, and fashioned by the Flemish sculptor Peter Scheemakers. The relief copy of the Poussin painting is contained within a rustic arch, and shows a woman and three shepherds, two of whom are pointing to a tomb. On the tomb is carved the Latin text Et in arcadia ego ('I am also in Arcadia' or 'I am, even in Arcadia'). The carving displays a number of small alterations from the original painting, and an extra sarcophagus has been placed on top of the main tomb. Above the Poussin scene are two stone heads, one showing a smiling bald-headed man, the other bearing a likeness to the goat-horned Greek god Pan.
Below the relief carving on the monument, an unknown craftsman carved the mysterious letters, eight on the first line, two on the second line, contained within the letters 'D M' on the second line. On Roman tombs, the letters 'D M' commonly stood for Dis Manibus, meaning 'dedicated to the shades'. The Shugborough Monument, however, is not a Roman tomb so this interpretation for D and M can be misleading.
In 1982, the authors of the pseudohistorical The Holy Blood and the Holy Grail suggested that Poussin was a member of the Priory of Sion, and that his Shepherds of Arcadia contained hidden meanings of great esoteric significance.
Speculation then grew that the inscription may encode secrets related to the Priory of Sion, or the location of the Holy Grail.