Work begins to preserve historic carvings at Royston Cave
Conservationists in Hertfordshire are working to preserve historic underground carvings.
Dating from the 14th Century, the wall carvings at Royston Cave feature a range of religious symbols.
Since its discovery in the 18th Century, the cave has experienced a marked deterioration in the detail of its carvings.
Experts believe the damage is being caused by worms feeding on nutrients in the chalk walls.
The cavern is man-made and in the shape of a beehive, with a small aperture at the top for ventilation.
It features an extensive range of wall carvings representing the crucifixion, the holy family and several saints, among them St Katherine, St Laurence and St Christopher.
Local historians have said the wall carvings suggest the Grade I-listed site may have been used by the Knights Templar.
The military order of the Roman Catholic Church was suppressed by papal edict almost 700 years ago.
Tobit Curteis, the conservation team leader, said two types of culprit worms had been identified - the 20mm-long purple eisenia foetida and the 8mm-long transparent dendrodrilus rubidus.
"We think the worms have leeched into the chalk over the last 200 years when water has been washed in from flooding," he said.
The team are now removing the worms' habitat - soil and debris - from the cave floor and injecting the walls with chemicals to strengthen them.
Mr Curteis said a cautious approach was being adopted by everyone involved in the project.
"The restoration work is very complicated, there's nothing like this anywhere in the country, so every piece of research we're having to do is from scratch.
"We can't have a second chance, if we get it wrong it will damage the cave, so we need to make sure that everything we do is stable and will work in the long term," he said.
The cave will be closed from 4 July until 15 July while the work is carried out.