A world-renowned stone circle in Orkney which is more the 4,000 years old has been vandalised.
Damage to the Ring of Brodgar includes graffiti which has been engraved into one of the stones at the Neolithic site near Stenness.
It is believed to have been caused sometime between Friday afternoon and Sunday morning.
Inspector David Hall said: “The stones at the Ring of Brodgar are priceless historical artefacts and the damage caused cannot simply be estimated in monetary terms.
“For someone to damage them in this way is a particularly mindless act.
“I would urge anyone who has visited the area over the last weekend to think back and if they believe they may have seen something suspicious, even if it didn’t seem of much note at the time, to let us know.
“We would also urge the public to continue to be vigilant at this site and report anything which could be of interest to police immediately.”
The Ring of Brodgar originally consisted of 60 stones, with 36 surviving today.
It is within the Heart of Neolithic Orkney Unesco World Heritage Site.
This also includes a large chambered tomb called Maes Howe, the Stones of Stenness and a settlement – Skara Brae.
The ring was built around 2,500-2,000BC and covers an area of almost 8,500 square metres.
It is the third largest stone circle in the British Isles – behind Avebury and Stanton Drew – and is the largest in Scotland.
One of the stones has already been vandalised, carrying a Norse runic inscription, while at least one other has been struck by lightning.
Celebrated visitors include Sir Walter Scott, who in 1814 wrote of the Ring of Brodgar and Stones of Stenness that “Stonehenge excels these monuments, but I fancy they are otherwise unparalleled in Britain”.
Historic Environment Scotland notes suggestions that the sites and monuments in the surrounding area were used for astrological observations from the Ring of Brodgar, but it is very hard to find conclusive evidence.
A Historic Environment Scotland spokeswoman said: “We were recently made aware of an incident of vandalism to the Ring of Brodgar.
“We would ask the public to be aware that causing reckless or deliberate damage to a scheduled monument is a criminal offence, and ask that anyone witnessing such acts report them to Police Scotland.”