One of the emblematic sights associated with Bulgaria is a group of barefoot men and women clad in traditional village costumes dancing over live embers. This is nestinarstvo, or firewalking, a supposedly Christian rite, where firewalkers dance themselves into a trance and eschew the perils of fire.

Now firewalking is performed at tourist locations and even in restaurants, but the only place to see the real thing is in the village of Balgari in the Strandzha. It happens on the night of 3 June, the high day of Ss Constantine and Helena.

Dancing on fire is in fact the visible tip of what in essence is a complex system of beliefs balancing between Christianity and paganism.

Some nestinari enter the fires carrying an icon of Ss Constantine and Helena believing that the saints will protect them from harm. Note the cloth that covers the icon

Ss Constantine and Helena are thought of as the patrons of nestinari. Icons with their likenesses have a central role in the nestinari worldview. They are present at all nestinari events throughout the year, not just on 3 June.

For most of the time these icons, dressed in cloths as if they were human, are kept away from people's eyes in a small nestinari chapel off the village square. They "go out" on special occasions only. The main one is on the Sunday preceding 3 June every year, when a procession takes them to an area known as Vlahov Dol. Here, the icons are "bathed" in the supposedly healing water springs and are taken back to their home, at Balgari.

Traditionally, three young men lead the nestinari procession on its way to the embers

In the morning of 3 June the ceremony gets repeated. Meanwhile, a bonfire is made in the village square. By the evening it has burnt down to glowing embers, ready for the firewalkers to come.

In the evening the village square gets full of people. The nestinari are inside the chapel, meditating. They believe their hearts and minds will be entered by none lesser than St Constantine himself who will provide them with guidance and strength.

Outside, bagpipes are playing and a drum beats the inimitable rhythm of nestinari music. A procession forms and heads to the embers. The most spectacular part of the rite begins.

Walking to the tune, nestinari start dancing around the fire. At irregular intervals some would take the icon above their heads and nimbly cross over the live embers.

The whole ceremony takes about half an hour. The nestinari dance in and out of the fire, the bagpipes and the drum measure the beat. Then, as if by the order of some unseen hand, the ceremony abruptly ends. The nestinari take the icons back to the chapel. The embers are still glowing. Some brave onlookers defy public orders and common sense, and jump into the fire – some with their shoes on, some without. You could tell who's had the best of luck by the way they walk out onto "firm ground" again.

The fire gets prepared for the dances

It is easy to spot paganism and Christianity in firewalking. But why were Ss Constantine and Helena picked to patronise the Bulgarian firewalkers?

Emperor Constantine and his mother Helena (who Bulgarians traditionally believe was in fact his wife) have been venerated throughout the Christian world for instituting Christianity in the Roman Empire. In the Strandzha, however, Christianity had to compete with a strong pagan tradition. There, the new religion and the old rites amalgamated in a curious manner. Where Rome sought to eradicate the old beliefs in many gods and deities, the Thracians in the Strandzha prudently used them to conceal their continuing veneration of the cult of the Great Goddess and her son and husband, the Great God. As centuries went by, the old gods became one whole with the Christian saints. The modern firewalkers are theoretically the heirs to the ancient priests of the Great God and the Great Goddess.

Nestinari step into the circle of fire protected by their faith only

In actual fact there is little hard evidence about the nestinari. Information about them started to emerge relatively late and was often self-contradictory. Modernisation, politics, the Orthodox Church and Communist atheism changed both the rite and the community that adhered to it for good.

The earliest reports about the nestinari are dated to the 1860s. Later ethnographers and anthropologists sought to interview the nestinari and research their rites, but were met with reluctance if not resilience: the nestinari would not discuss their beliefs with outsiders. Up until the middle of the 20th century few researchers managed to interview nestinari or be present at a firedancing ritual.

The rite is also not exclusively Bulgarian – it was practised by both Bulgarians and Greeks living in the Strandzha. When the Balkan borders changed in 1912-1913 the Greeks from the predominantly Greek villages of Kosti and Brodilovo left. They carried their nestinari icons and drums with them. Their great-great-grandchildren now live in northern Greece, and still do their anastenaria dances.

In Bulgaria, it took the officially atheist Communist authorities just a few years to hurl the nestinari into oblivion, as their "dark superstitions" were seen as incompatible with the Communist idea of establishing a rational society. The number of nestinari dwindled.

Things started to change in the 1970s, when Communist Bulgaria became more nationalistic. The new sentiment was endorsed by none lesser than Lyudmila Zhivkova, the daughter of Communist leader Todor Zhivkov. Her ideas of Bulgarian "uniqueness" and her penchant for mysticism and occultism, resulted in a renewed interest in the nestinari. Their rite was both spectacular and could easily be packaged into a tourist product. Trained firewalkers appeared as entertainers at the large tourist resorts along the Black Sea coast to perform in front of hard currency paying visitors.

Following the collapse of Communism in 1989 firewalking in the Strandzha got a new impetus. In 2009 it was inscribed on the UNESCO list of intangible world heritage.

In the 2010s, the nestinari event in Balgari village has turned into a media event

However, what you will see in the village of Balgari on 3 June now is a far cry from the original nestinari rite. Modern firewalking is mainly a show being videoed on cameras and smartphones. The 3 June event has little to do with contemplation and mysticism. It is a village fair with the usual assortment of food stalls, grills and beer.

Still, taking in the 3 June ceremony in the village of Balgari is by all means a rewarding experience not least because it will pose more questions than give answers. Where and when did the nestinari originate? Why? Are there any links between the Strandzha nestinari and similar rites in ancient Rome, the Middle East and later in China? Is it a form of shamanism? Does it really incur a spiritual trance? Or is it an ancient medicine for psychological pain?