The highly controversial Toro de Jubilo fire bull festival took place in Medinaceli, Spain, this weekend.

Toro de Jubilo
A bull with flaming balls of tar attached to its horns runs in the bull ring during the Toro de Jubilo festival in Medinaceli, Spain. The body of the animal is covered with mud to protect it from burnsGonzalo Arroyo Moreno/Getty Images

In an ancient pagan tradition thought to date from the bronze age, a bull is tied to a post in the middle of the bull ring and balls of tar and pitch are attached to its horns and set alight.

Local men then take it in turns to taunt the anguished bull and get it to chase them. The bull is covered with a thick layer of mud to protect it from the burning liquid that rains onto its face and back.

Toro de Jubilo
A bull tries to resist as is it tied to a post so that the flammable balls attached to its horns can be set alightGonzalo Arroyo Moreno/Getty Images
Toro de Jubilo
Gonzalo Arroyo Moreno/Getty Images
Toro de Jubilo
A man restrains a bull as another ignites the balls of tar and pitch attached to its hornsGonzalo Arroyo Moreno/Getty Images
Toro de Jubilo
Gonzalo Arroyo Moreno/Getty Images
Toro de Jubilo
Gonzalo Arroyo Moreno/Getty Images
Toro de Jubilo
A reveller uses a jersey as a cape in front of a bull with its horns on fireGonzalo Arroyo Moreno/Getty Images
Toro de Jubilo
Gonzalo Arroyo Moreno/Getty Images

Animal rights rights activists tried to stop this year's festival, attaching themselves to the post in the middle of the bull ring.

Festival supporters tried to stop them, and fights broke out. The police intervened, arresting some of the animal rights activists.

The protesters' attempts to stop the festival were in vain, merely delaying its start by an hour.

Toro de Jubilo
Police officers cordon off animal rights activists blocking the bull ring to boycott the Toro de Jubilo fire bull festivalGonzalo Arroyo Moreno/Getty Images
Toro de Jubilo
Police officers try to remove animal rights activists blocking the bull ringGonzalo Arroyo Moreno/Getty Images
Toro de Jubilo
A Toro de Jubilo supporter bites the hand of an animal rights activistGonzalo Arroyo Moreno/Getty Images

A bull named Islero was restrained by a group of men as a pole with two large torches on it was strapped to its horns.

A crowd cheered as young men taunted the animal, trying to get it to charge them. Once the balls of tar had been consumed by the flames, fireworks exploded around the bull.

Toro de Jubilo
Fireworks explode around a bull after the flames on its horns have gone outGonzalo Arroyo Moreno/Getty Images
Toro de Jubilo
Fireworks explode around a bull after the flammable balls attached to its horns have gone outGonzalo Arroyo Moreno/Getty Images

To the people of Medinaceli, the festival is a culturally important link to the past that should be protected by Unesco.

People for the Ethical Treatment of Animals have called on Spanish authorities to ban the festival. Peta spokesman Ben Williamson said: "The fiery balls burn the bulls' horns, eyes and other parts, causing huge stress. The agony they must suffer is unimaginable."