Every year, on January 17, the people of San Bartolome de Pinares, in Spain, celebrate St. Anthony by riding their horses, donkeys and mules through piles of burning tree branches in a celebration called Las Luminarias.

The unique tradition of leaping over and through flames dates back 500 years, but the men and women of San Bartolome de Pinares village still celebrate it religiously. They gather all the branches they find in the days leading up to the festivities, and when dusk falls on the eve of Saint Anthony’s, they light them ablaze. Riders lead their mounts through the burning piles of the village, accompanied by sounds of drums and Spanish bagpipes.

Jumping through the flames is said to bring the animals the protection of St. Anthony Abad, acknowledged as the patron of domestic animals, ever since the Middle Ages. Locals believe the fire purifies their animals and protects them against illnesses, all year long.

“This comes from thousands of years ago. So that animals did not get unwell, the old priests would bless them with fires so that they would jump and be purified,” one local said.

Animal rights activists don’t buy the whole purification deal, but in a country like Spain, where traditions like bullfighting, Shearing of the Beasts or Day of the Geese, they don’t have too many hopes of putting an end to it. Still, many are at least willing to try.

“There is no logic in forcing these animals into a stressful situation against their own nature. In the midst of the 21st century, this is something from a bygone era. There is no superstition or belief that should justify an act of such cruelty,” Juan Ignacio Codina from the Observatory of Justice and Animal Defence, said.

The owners say their animals remain unharmed during the procession thanks to precautions taken by riders to cut their hair to avoid burns. A few years back, the mayor of San Bartolome de Pinares told reporters that veterinarians checked the horses after Las Luminarias and couldn’t find a single burn mark, or anything else wrong with them.

One thing that even the more stubborn locals will agree with is that Las Luminarias has become too much of a spectacle in recent years. Before, the shrubs and pine branches used to light the fires used to be much smaller, but nowadays they are brought in by trucks, and the fires are much bigger to impress spectators. Many would prefer to return to the old ways of animals walking over smaller fires, not jumping through flames.