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STONEHENGE, England — King Arthur rallied his band of warrior-druids at one of the most sacred sites of the ancient world.

He was readying them for battle.

Dressed in white robes, carrying swords and staffs, and occasionally checking their iPhones, his religious order gathered under the towering megaliths of Stonehenge, a monument constructed more than 4,000 years ago in the English countryside.

"If you're going to stand up for truth, honor and justice, you've got to fight in any arena — and I fight in every arena," Arthur said, his silver mane fluttering under his pagan crown.

This was not 1,500 years ago — when the King Arthur of legend is said to have lived — but a blustery, drizzly morning last week.

And leading the ceremony was not the King Arthur, but a 62-year-old man who was born John Timothy Rothwell. Thirty years ago, Rothwell became convinced he was the reincarnation of King Arthur and legally changed his name to King Arthur Uther Pendragon.

It even says so on his passport.

Before this transformation, he was a British Army soldier and a member of a biker gang. Now he is a pagan priest, a sword-bearer and the chieftain druid of this anachronistic creed.

"Every day, I wake up Arthur, I go to sleep Arthur. I wake up a druid, I go to sleep a druid," he said.

NBC News visited him and a few dozen of his followers as they gathered at Stonehenge for the spring equinox last week. Halfway between the shortest and longest days of the year, this was one of the most important events in the druid calendar.

Arthur is one of some 4,000 people who identify themselves as druids in the U.K., according to government figures. But the origins of this faith and its connection to Stonehenge are hard to pin down.

A druid prays in the inner circle of Stonehenge as a visitor checks her cellphone during the spring equinox at Stonehenge. Carolina Reid / NBC News

The first druids were Iron Age priests who lived thousands of years ago among the Celtic tribes of Britain. But hardly anything is known about these people, their beliefs or practices. Modern druidism is largely based on the works of 17th and 18th-century writers who revived and romanticized the concept.

The religion has no sacred texts or set rituals, so its costume-wearing acolytes follow a loose ideology of worshiping deities that share a connection to the Sun, Earth, plants and animals.

These themes were at the center of last week's ceremony, attended by more than 100 people, including druids, hippies and tourists.

"We were chanting, and we were honoring the union of the Earth and the Sun. Without them you wouldn't have a spring, and without a spring you wouldn't have a summer," Arthur explained afterward. "It's how life is formed and made, so anything that is making life is divine to all."

King Arthur Uther Pendragon Carolina Reid / NBC News

No one knows for sure who built Stonehenge, nor how or why they transported the 30-foot, 40-ton stones to this patch of land.

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Nevertheless, it is a UNESCO World Heritage Site that the organization calls "the most architecturally sophisticated prehistoric stone circle in the world."

The link between Stonehenge and the druids is tenuous. It was John Aubrey, a 17th-century writer and philosopher, who first claimed the site was a druid temple, but this has never been confirmed.

Last week's ceremony wasn't all peaceful worship however — Arthur was also there to declare war. Not on some mob of marauding knights, but against the government-backed charity that manages the site — a dispute over the price for parking.

"My order is the political-warrior arm of the druid movement, so we take on court cases and fight the government when we feel the government is wrong," he said.

King Arthur Uther Pendragon knights a fellow druid. Carolina Reid / NBC News

As an eco-warrior, he has been arrested dozens of times in relation to various alleged missteps committed by officialdom around Stonehenge. He has also run for election to the British Parliament several times — polling in last place with 729 votes at the last attempt in 2015.

His current fight is against the charity English Heritage, which runs Stonehenge, for its decision to charge £15 (about $18) for parking during the wildly popular summer solstice. This is a hike from the regular price of £5 (around $6).

With around 40,000 people flocking to the monument on June 21 each year, the charity says the increased fee is to encourage carpooling. But Arthur claims that charging worshipers more on their sacred day amounts to discrimination against their faith.

He accuses English Heritage — or "English Heretics," as he calls them — of enforcing a "pay-to-pray" policy.

"They are charging us more to turn up for our holy days than they would charge us to turn up as a tourist," he said.

English Heritage disagrees.

"A wide range of people enjoy coming to Stonehenge for summer solstice," it said in a statement last year after the first parking charge was imposed. "All of those who drive there are charged a parking fee — just as they might be if visiting other sites, whether religious or not."

A line of RVs and trailers parked outside the entrance of Stonehenge. Carolina Reid / NBC News

Arthur, who has no income and lives solely off donations, has a court date with English Heritage on May 24 and plans to argue his case under the European Convention of Human Rights. He made reference to the dispute during his ceremony last week, a jarringly administrative passage in an otherwise rousing homily.

"I have taken them to court under Articles 9, 10, 11 and 14 of the European Convention and I've got a full day's hearing on the 24th of May," he informed the crowd, his tone shifting momentarily from high-priest to one reminiscent of a local government official.

"They make a fortune out of this and they still want to charge us to come here and worship. It's obscene," Arthur added. "It's ridiculously lucrative. It's the biggest cash cow they've got."

This slip into the mundane adds to the sense that, despite the attempts at creating a sacred ambiance, the outside world is always creeping into the periphery at Stonehenge.

Surprisingly close to the monument runs the A303 highway and its constant hum of busy traffic. A handful of police officers in fluorescent jackets patrol the perimeter. And, like any pop concert, the pagan ceremony is accompanied by a sea of cellphone screens, raised aloft to capture the ritual for social-media posterity.

Druids and tourists participate in a ceremony at Stonehenge on March 20. Carolina Reid / NBC News

Arthur's personal story also blurs the boundary between the holy and the everyday.

The son of a sergeant in the British Army, he joined the military but left after he was injured in a skydiving accident. He then fell into the world of biker gangs, forming a motorcycle club called the Gravediggers in the early 1980s.

He was first drawn to the occult after a "near-death experience" aged 14. He said the incident sparked "the beginning of his druidic training."

But it wasn't until he read a book on King Arthur in the 1980s that he began to draw comparisons between the mythical leader's life and his own, eventually leading him to believe he was the king incarnate.

"There ain't much difference between a bike club and this — think about it!" he told NBC News, pointing at the medieval scenes around him. "The only difference is I'm now on an iron horse. So it's exactly the same."

A druid participates in a ceremony at Stonehenge. Carolina Reid / NBC News

He seemed reluctant to offer any more explanation for the link other than to say that he was carrying on King Arthur's work of fighting injustice.

Beyond the folktales that have now been co-opted into Hollywood, historians have been unable to find any evidence that King Arthur actually existed at all.

The modern-day version said he has always felt a connection to something.

"Most children walking through the woods pick up a stick and pretend it's a rifle. I picked one up and pretended it's a sword," he said. "I've always had a knowledge that I was from a different time."

But fragments of his old life live on. After the ceremony, he packed away his robes and tin crown, put on his helmet, and rode away on his bright yellow motorcycle.

King Arthur Uther Pendragon, left, and Merlin speak beside his motorcycle at Stonehenge on March 20. Carolina Reid / NBC News

Among his followers is Merlin, a 44-year-old from west London who gave up his life as a construction worker to follow the religious order.

Formally known as Jason, he's swapped his hard hat and overalls for a white robe, wizard's beard and a ceremonial staff topped with a large quartz crystal.

"I've been coming here since 1981," he said in almost hushed tones. "It's very different to the city, much more peaceful."

Despite the pre-dawn calm, Arthur seems to relish his adversarial relationship with the authorities. And he said he has no plans to yield this battle any time soon.

"Stonehenge is always under threat from something or other," he added. "And there's hopefully someone who's going to fight to keep it right."

Until Arthur's next incarnation, that someone is him.