Once every winter, thick smoke begins to swallow up the houses in this village in the barren lands of Avila, northwest of Madrid. It means the town's bonfire festival honoring St. Anthony the Abbot has begun.

The music of a small bagpipe and a drum drift through the gloom. Then comes the clack of hooves on the cobblestone street. Suddenly, the flames roar up and horses and riders emerge to begin leaping through the flames.

St. Anthony the Abbot is the patron saint of domestic animals, and some townspeople say the celebration dates back five centuries to when the plague was fought with Roman Catholic rituals that used the smoke for purification.

San Bartolome de Pinares has kept its "luminarias" festival alive with religious intensity and unswerving pride, fending off criticism from animal rights groups.

When agriculture was far more important, mules and donkeys also were led past the bonfires in a purifying ritual. Now, horses are the only animals used.

In recent years, tourists, journalists and photography aficionados have put attention on the ritual, which has come under attack from animal rights groups.

"There is no logic in forcing these animals into a stressful situation against their own nature," said Juan Ignacio Codina, one of the most vocal critics of the "luminarias" festival. "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."

Codina's group, Observatory of Justice and Animal Defense, contends the "luminarias" break regional and national laws of animal protection and public entertainment shows and it filed a complaint with the regional government in 2013.

The government of Castille and Leon, the region where San Bortolome sits, replied that veterinarians sent by authorities couldn't find any injuries on the horses from the bonfires.

"Not one burn, not even one harmed horse," said the mayor, Maria Jesus Martin, who insists that no horse is forced to jump over the frames.

"It makes me angry to hear the insults without those speaking knowing anything at all about the tradition," she said. "They call us stubborn, hicks. They have even openly called on social media to throw me, the mayor, into the bonfire."

Still, some in the village of 600 people think it would be better to return to a more moderate version of the festival. They say branches of pine and shrub for the bonfires used to arrive in small quantities on the backs of donkeys, but now the fuel is hauled in by trucks and the bonfires are much bigger and the smoke thicker.

Some people also would like to see a halt to the controversial jumping of the bonfires, since the original tradition only envisioned purifying the animals by walking them around - and not over - the flames.