A plan to cover 3,000-year-old cairns on Exmoor with fabric to help protect them has been rejected.
The trust will be able to use do some covering work
The National Trust applied for planning permission for the scheme on Dunkery Beacon, but this was turned down by the National Park Authority.
The Trust wants to cover the cairns with a fabric, which would then be covered with stone and seeded with heather and moorland grasses.
But the Park Authority said it was "unconvinced" about the idea.
Chris France, head of planning and community, told BBC News Online: "The majority acknowledged that some repair and action was needed, but were unconvinced about covering.
"They felt that you wouldn't then be able to see the archaeology, which is an essential part of the area.
"The plans were not refused outright: the trust can do some covering work on one of the mounds to see it if is successful, and repairs to another."
The National Trust says the cairns, located on the highest and most exposed point within the National Park, are being damaged by people removing stones.
Chris Hewitt, National Trust property manager, said: "The Trust has three months in which to appeal, if it chooses to do so, but we are seriously worried that the fragile status of the cairns may seriously deteriorate over the forthcoming winter months."