Smoke and flames filled the night in San Bartolomé de Pinares, a central Spanish town of some 600 inhabitants, in the annual festival held on Thursday, the eve of Saint Anthony's Day for the patron saint of animals.
One by one, horses and their riders jumped the flames of large bonfires lit in the narrow, paved streets of the town, some 100 kilometres (60 miles) northwest of Madrid.
"No one knows how old the tradition is. My grandfather told me that his great-grandfather took part," said 34-year-old Diego Martin, this year's patron of the festival of "illuminations".
"They say it could be 300 or 400 years old," said Martin, this year's festival patron, as he sat astride a Spanish horse, Fiel, and opened a procession of some 150 riders.
The town is fiercely attached to the festival, said by some to date back as much as 500 years, despite opposition from animal rights groups concerned about the safety of the horses.
Just a few days earlier, Spain's National Association for the Welfare of Animals asked the townspeople not to let their horses leap over the fires, apparently to no avail.
The horses, blessed before the festival, wear their manes and tails carefully plaited to prevent them catching fire as they jump over the centre or, in many cases, the sides of the bonfires, which have been sprinkled with water to produce more smoke.
"There was an epidemic that killed all the horses in the town. Since then, we have done this to purify them, to keep them from any evil by asking for the protection of the saint," explained 20-year-old Libertad Gómez, one of the few women riders, who has been taking part for seven years.
"More than a tradition, for us it is a feeling. It is something you live almost since you were born," said Libertad, who rode with dozens of others through the streets to be engulfed by the "saint's smoke".
Indeed, the smoke is so thick it stings the eyes and lends a ghostly aspect to the horse and rider as they leap the fires.
That does not stop youngsters taking part in a tradition passed down from father to child, such as 10-year-old Alejandro Nunez, who jumped for the second year running on a white horse.
"I really like it. At first, it was a bit scary but that goes," he said, equipped with a helmet and a checkered scarf to protect him from the smoke.
"A lot of people let go of the reins so the horse can decide. If the horse does not want to jump, it does not jump. It goes around the side," said Martin, who began riding at the age of four.
Other townspeople similarly reject accusations that the festival is cruel.
"The horse does not suffer," said Diego Martin, the festival patron.
"We have never had any accidents other than a horse slipping and falling but never because of the fire. They are our animals and we have the greatest interest in them not suffering any harm," Martin added.
Horse tamer Igor Villa, a regular participant, agreed.
"Sometimes they are a bit scared, it depends on the animal. But there is no danger to them," he said, dressed in a jacket and brown riding trousers as he sat astride a Spanish grey horse.