Scrambler motorbike riders have inflicted damage on an ancient 3,000 year old ring cairn near Swansea.
Witnesses have spoken of their horror at seeing riders of illegal off-road bikes using the historic ring cairn at Tor Clawdd, Mawr, as a circuit, causing significant damage.
Police officers attended the scene and have now pleaded with those responsible to think of "the consequences of their actions."
The ancient monument is the remains of a ring cairn of earth and stone, believed to date back to the Bronze Age.
Ancient Monuments UK, an online database of historic monuments, describe it as being of "national importance for its potential to enhance our knowledge of prehistoric burial and ritual practices" and "an important relic of a prehistoric funerary".
Those responsible have not been identified, as their bikes have no registration plates and their faces are covered, villagers say.
Officers from Welsh ancient monuments body Cadw are liaising with the local commoners’ association, Glamorgan Gwent Archaeological Trust, residents in the area and South Wales Police to install signage, arrange repairs to the monument and discourage further damage.
Former councillor Ioan Richard hit out against those responsible.
He said: "These scramblers are not only destroying an ancient Cadw listed structure, they are also destroying the grazing sward and seriously disturbing hill grazing livestock with lambs and calves getting separated from their mothers.
"A serious economic matter for hard working struggling hill farmers."
Scrambler motorbikes have caused much unrest for residents in many different areas of Swansea, including those living in Manselton, Brynhyfryd and Gendros, who have said motorised menaces are making their lives hell.
Vandals have also damaged Wales's most famous Roman ruin :
A South Wales Police spokeswoman said: "We received a report on June 13 of damage being caused around Tor Clywdd – officers attended and no off road bikes were present at the time.
"Off road biking continues to be a concern for our communities and we continue to patrol key locations and take action when appropriate.
"We would urge people to think about the consequences of their actions.
"Anyone with information re this incident should contact 101 quoting occurrence 2000208111."
