Named for the patron saint of Pamplona, Sanfermines has roots dating back to the Middle Ages in the Spanish region of Navarra. The festival evolved from the religious ceremonies held in honor of San Fermín in the 12th century, combined with later trade fairs held in the region and, of course, bullfights, which were first documented in the 14th century. Though initially held on October 10, the celebrations were moved in 1591 to July to coincide with the annual fair (and avoid the inclement October weather). By the 17th and 18th centuries, the festival included music, dancing, acrobatics, as well as bullfights; later spectacles included fireworks displays, exotic animals and a parade of giant papier-mâché heads known as the Comparsa de Gigantes y Cabezudos (Parade of Giants and Big Heads).

At the heart of the eight-day festival is the encierro, when about a dozen bulls are released from their corral just outside Pamplona’s medieval stone wall at 8 o’clock each morning. The mighty animals—some weighing more than 1,500 pounds—then rush through cobblestone streets and alleys to the city’s central bullring, where they will participate in that evening’s corrida (bullfight). Thousands of human runners accompany them on the 825-meter distance, cheered on by the spectators who line the streets. The run usually lasts between three and four minutes, but can take as many as 10, especially if one of the animals loses his way and gets isolated from the others.

Dozens of people are injured each year during Sanfermines; many trip and fall, but others are gored by one of the massive bulls. During last month’s festivities alone, there were six gorings and 48 hospital cases. Since recordkeeping began in 1924, bulls have killed a total of 15 people in Sanfermines. Despite—or perhaps because of—its element of danger, the festival has become internationally famous, thanks in no small part to its romantic portrayal in Ernest Hemingway’s “The Sun Also Rises,” known in the Spanish-speaking world simply as “Fiesta.” Hemingway first visited Pamplona in July 1923, with his first wife, Hadley Richardson. He became fascinated by bullfighting and bullfighters, and returned to the festival numerous times, including his last visit in 1959. As a correspondent for the Toronto Star, the young writer actually took part in the encierro in 1924, and a false rumor spread that he had been gored by one of the bulls. Hemingway’s writings helped build the festival’s fame worldwide, and drew an ever-more international audience to Pamplona’s streets each year.

Organizers of the Great Bull Run now plan to bring the excitement from Pamplona to the United States, and from cobblestone streets to drag-racing strips and horse racing tracks. The first event will take place on August 24 near Richmond, Virginia; a second is planned for October in Conyers, Georgia. Some 5,000 people have already signed up for the Richmond run, and organizers expect a similar number—or more—for the Georgia event. Future runs are planned for sites in Texas, Florida, California, Minnesota, Illinois and Pennsylvania.

To address safety concerns, the Great Bull Run’s regulations include a minimum age of 18 for participants and no alcohol is permitted. In addition, a series of gaps (or “coves”) will be provided in the course’s fencing to allow participants to escape during the runs. The bulls used will also be locally bred and less aggressive than Spain’s fighting bulls, and participants are prohibited from touching the animals during the run. Despite these precautions, the event’s website warns: “By participating in the run, you accept the risk that you might be trampled, gored, rammed or tossed in the air by a bull, or bumped, jostled, tripped or trampled by your fellow runners….Make no mistake: You could get seriously injured in this event.”

Along with bullfighting in general, bull runs such as the ones in Sanfermines have long provoked controversy. Animal rights groups have raised serious concerns over the treatment of the bulls used in runs and fights, arguing that the animals are tortured and killed for entertainment. In 2012, Catalonia (which includes Barcelona) became the second Spanish region to ban bullfighting entirely. For their part, organizers of the Great Bull Run have stated that the bulls that run in their events will not be killed or abused in any way, and that a veterinarian will be on site to regularly check the animals’ health. Despite these assurances, the Humane Society has expressed concern, calling the events “a shameful example of cruelty for the sake of nothing more than entertainment and profit.”