(CNN) — Hundreds of protective marks designed to ward off evil spirits have been found scratched into the walls of an English cave system.
The significance of the signs, which had previously been written off as graffiti, was noted by eagle-eyed visitors to Creswell Crags in the East Midlands, central England.
"These witches' marks were in plain sight all the time!" John Charlesworth, the tour leader at the time, said in a statement. "Being present at the moment their true significance was revealed will stay with me forever."
The protective marks were carved by superstitious locals hoping for protection.
The marks were identified in October and academics have been studying them since.
It is not yet known when these particular marks were made, but other apotropaic marks -- designed to deter harmful or evil influences -- have been found in houses built between around 1550 and 1750.
Experts say similar signs were scribed into churches and homes, as well as other caves, and were used to ward off sickness, death or poor harvests.
Marks include VV -- thought to be a reference to Mary, Virgin of Virgins -- and PM, or Pace Maria, a call for peace from the Virgin Mary.
There are also diagonal lines, mazes and boxes, which are thought to have been used in an attempt to "trap" evil.
This may be the biggest concentration of apotropaic marks ever found in Britain, and experts say it is unprecedented in number and variety.
"I cannot emphasize how important this corpus of apotropaia is to graffiti research, I think off the top of my head, it is the largest number of examples found anywhere and in any context in the UK," said Alison Fearn, of Leicester University, who studied protective marks as part of her doctorate.
Apotropaic marks, from apotrepein, the Greek for "to turn away," were possibly carved by superstitious locals worried about what might emerge from the caves.
The apotropaic marks include references to the Virgin Mary.
"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," Duncan Wilson, chief executive of Historic England, said in the statement.
"We can only speculate on what it was the people of Creswell feared might emerge from the underworld into these caves."
The site is also known as the home of Britain's earliest cave art, after 13,000-year-old cave paintings were discovered in 2003.
"Creswell Crags has already amazed the 21st century with its revelations of Palaeolithic designs," said Professor Ronald Hutton, an authority on folklore.
"Now it does so again with a fresh one of medieval and early modern ritual protection marks on a huge scale, making a very important contribution, at a stroke, to one of the most significant current areas of new scholarly research."