Hundreds of "witches' marks" to prevent evil spirits rising from the underworld have been discovered in caves at a limestone gorge, experts said.
The find, carved on walls and ceilings of the caves at Creswell Crags on the border between Nottinghamshire and Derbyshire, is thought to be the largest collection of its kind in one place in the UK.
The discovery was made by enthusiasts Hayley Clark and Ed Waters, from the Subterranea Britannica group, during a cave tour when they noticed the rare protection marks on the walls.
The marks were previously thought to have been graffiti from the time before the caves were shut off.
Witches' marks, or "apotropaic" marks, from the Greek word apotrepein, "to turn away", are most commonly found in historic churches and houses, near doorways, windows and fireplaces, to protect the inhabitants from evil spirits.
Experts said the number and variety of the marks found in the caves is unprecedented.
Among the most common are the double VV engravings, thought to reference Mary, Virgin of Virgins, and PM or Pace Maria, while other symbols are believed to be devices for capturing or trapping evil, including diagonal lines, boxes and mazes.
The marks appear to have been added to over time and may indicate a need to strengthen the protection against underworld spirits in response to unexpected sickness, death or poor crops, the experts said.
Until now the largest known quantity of witches' marks in caves in Britain was 57 in Somerset, but the number at Creswell Crags is far higher – with hundreds in one cave alone and marks now found in all the caves at the site.
There may even have been more in the past, as the caves were excavated by archaeologists during the 19th century and were widened in the process, potentially accounting for some surfaces featuring no marks.
It is the latest significant discovery at the caves, which provided shelter for Neanderthal and anatomically modern people through a crucial period of human evolution between 130,000 and 10,000 years ago.
The site has been a rich source of archaeological finds and even features Britain's earliest cave art, with 13,000-year-old pictures of birds, deer, bison and horses.
John Charlesworth, heritage facilitator and the tour leader at the time of the discovery of the protective marks, said: "These witches' marks were in plain sight all the time.
"Being present at the moment their true significance was revealed will stay with me forever. This remarkable place continues to give up its secrets."
Academic and TV presenter Professor Ronald Hutton, an authority on folklore, said: "This discovery is significant because it looks like the largest assemblage of protective marks ever found in British caves, and possibly anywhere in Britain.
"This is a suddenly a large new area of research for historians and archaeologists, and so adds appreciatively to the importance of the Crags as a world resource."
The team who look after Creswell Crags are now working with academics and experts from Historic England to better understand the significance and extent of the discovery at the site, which is a scheduled monument.
Duncan Wilson, chief executive of Historic England, said: "Creswell Crags is already of international importance for its Ice Age art and ancient remains.
"To find this huge number of protection marks from the more recent past adds a whole new layer of discovery.
"Even 200 years ago, the English countryside was a very different place; death and disease were everyday companions and evil forces could readily be imagined in the dark.
"We can only speculate on what it was the people of Creswell feared might emerge from the underworld into these caves."
Creswell Crags will be launching tours of the areas containing witches' marks for the first time, from late February.