The festival of San Fermín, held every July in Pamplona, Spain, since the 16th century, has its origins in religious tradition, honoring a Catholic saint now nearly 2,000 years martyred. But the celebrations have become increasingly secular over the years, with round-the-clock revelry—and nostalgia for a world Ernest Hemingway so vividly painted in The Sun Also Rises—drawing visitors from around the world.
The festival’s most enduring legacy is the running of the bulls, or encierro, from the Spanish word for to corral or enclose. Held on the second day of the festival, July 7, the encierro consists of letting loose a small number of bulls in the city streets while transporting them to the bullring for bullfighting. Though it takes place during several festivals, the encierro at San Fermín is the most world-renowned.
The running of the bulls and ensuing bullfight have been the subject of criticism from animal rights groups like PETA, which say it tortures animals for human entertainment. But it's not just the animals whose lives are endangered. In 1947, when LIFE sent photographer Tony Linck to document the mayhem, two bull runners—men who run in front of the bulls—were gored, and the crowd was too enraptured with the bedlam to notice:
For a week gay blades stay up all night dancing and drinking, then gather at 7 o’clock in the morning for the encierro, the bull run. Yelling and jostling, they lead the bulls in a mad dash through the street toward the bullring. Last month’s fiesta was such a gay affair that almost nobody noticed when two of the encierro runners were killed by the bulls.
More than a dozen people have died during the festivities in the last century. Consequently, several safety measures have been established to improve the safety of revelers, including rules banning poor footwear, inebriation and harassing the bulls during the run. But there will always be more than a hint of danger in the annual tradition. The danger, of course, is part of the fun.
Liz Ronk, who edited this gallery, is the Photo Editor for LIFE.com. Follow her on Twitter @lizabethronk.