Security is being reviewed at a Staffordshire stately home after vandals damaged a historic monument.
Vandals climbed on top of the monument
A gang of youths climbed on top of The Shepherd's Monument at Shugborough Hall and smashed ornamental sea shells at about 1500 BST on Tuesday.
Experts were called in recently to examine an inscription on the 250-year-old monument rumoured to reveal the location of the Holy Grail.
A spokesman said the vandals may have caused irreparable damage.
"The Shepherd's Monument is of international importance, both as a work of art and because of the legend that a baffling inscription on the monument provides clues to the true location of the Holy Grail," said the home's general manager Richard Kemp.
He said the vandals were disturbed by gardeners and ran off across Essex Bridge in the direction of Great Haywood.
"Security at Shugborough is now being reviewed, although there are currently routine and random patrols at all times," added Mr Kemp.
A spokesman from Staffordshire Police said: "This was a mindless attack and we would appeal for anyone with information to come forward."