A secret site for the Knights Templar?

In a hole in the ground beneath the Hertfordshire market town of Royston, dimly illuminated by flickering light, I was looking at a gallery of crudely carved figures, blank-faced and bearing instruments of torture. Cave manager Nicky Paton pointed them out to me one by one. "There's Saint Catherine, with her breaking wheel. She was only 18 when she was martyred," Paton said, cheerfully. "And there's Saint Lawrence. He was burnt to death on a griddle."

Amid the grisly Christian scenes were Pagan images: a large carving of a horse, and a fertility symbol known as a sheela na gig, depicting a woman with exaggerated sexual organs. Another portrayed a person holding a skull in their right hand and a candle in their left, theorised to represent an initiation ceremony – a tantalising clue as to the cave's possible purpose. Adding to the carvings' creepiness was their rudimentary, almost childlike, execution.

Imagine the surprise, then, of the people who rediscovered Royston Cave, quite by accident, in the summer of 1742. A workman, digging foundations for a new bench in the town's butter market, struck a buried millstone and found that it was hiding the entrance to a deep shaft in the earth. This being an age before the dawn of health and safety directives, a passing small boy was promptly handed a candle and sent down on a rope to investigate, while the townsfolk of Royston chattered excitedly above about the prospect of buried treasure.

What was discovered was less lucrative but far more mysterious: a broken cup and some jewellery, a human skull and bones, and walls engraved from top to bottom with strange expressionless figures. Three centuries later, Royston Cave remains one of Britain's most mysterious places, with ever more theories as to its purpose leading no closer to an answer.

There are, however, plenty of theories. Those of an esoteric disposition have claimed that the cave lies at the intersection of two ley lines – ancient pathways theorised to connect places of spiritual power – one of which, the so-called Michael Line, also runs through Stonehenge and Avebury.

More easily verifiable is the fact that the cave lies directly beneath the intersection of two highly significant ancient roads: the Icknield Way, a historical trackway that runs along southern England's chalk escarpment from Norfolk to Wiltshire; and Ermine Street, a Roman road that originally ran from London to York. A large footstone is now all that remains of a cross that once stood at the junction of these two roads, named for Lady Roisia, a local noblewoman after whom Royston is thought to have been named.

The antiquarian William Stukeley, who visited Royston a couple of months after the cave's rediscovery in 1742 and wrote an early study as to its purpose, noted that such crosses were common at major junctions, and served two purposes in an age of high religiosity and low literacy: "To put people in mind of saying their prayers; and of directing them in the road they wanted to go." Holy people would, he wrote, build "cells and grottos in rocks and caverns, and by highway sides", directing travellers and praying for them. A prominent carving in the cave depicting Saint Christopher, patron saint of travellers, lends credence to the theory that the cave served as this kind of hermitage.

BBC