The first time my friend Rob and I experienced Pamplona’s San Fermin festival was in 2017. Held every year from 6-14 July in the northern Spanish city, it’s most famous for its bull runs, or encierros: at 8 a.m., on eight consecutive mornings, the six bulls destined for that evening’s bullfight, as well as six docile oxen to guide them, run for almost a kilometre through Pamplona’s oldest quarters, accompanied by thousands of thrill-seeking human participants known as mozos.

Rob and I have now run with the bulls of Pamplona four times – once that first year, once in 2018 and twice at last year’s festival (it was cancelled in 2020 and 2021 because of Covid). Next week we’ll be meeting in Pamplona again, to run our fifth and sixth encierros. If our girlfriends ever join us for San Fermin, which so far they haven’t, their reaction to how much we discuss our runs – tactics beforehand, minute analysis afterwards, starting at 8.05 a.m. over the best pint in the world – will probably be incredulity quickly followed by boredom.

But there’s a lot to talk about, because several factors make it extremely difficult to run the world’s best-known encierros. Some of these are inherent to the tradition of bull-running itself, which started in Spain in the Middle Ages, as an offshoot of farmers herding their cattle from the countryside into town for bullfights or markets; others, though, are unique to Pamplona’s annual fiesta, during which more than a million visitors descend on the city for the 24-hour street parties, bullfights and bull runs, live music, fireworks and parades.  

The bovine protagonists of most encierros, including Pamplona’s, aren’t the kind of bulls you’d encounter in a British field: they are toros bravos, a species reared specifically for the bullring on vast, wild plains called dehesas. They are much more powerful and aggressive than any other species of bull, and despite weighing half a ton when they’re ready for the ring (at four years old), can run at astonishing speed.

It usually takes the bulls between two and two-and-a-half minutes to complete Pamplona’s 848-metre course, although the fastest encierro on record (7 July, 1975) was over in just 1 minute and 50 seconds. An analogy might help here, because describing their speed as one sees it on the street is impossible (nor is it captured by the YouTube videos). The world record for 800 metres, held by Kenya’s David Rudisha, is 1:40; if Rudisha continued that pace over the extra 48 metres, he’d run the Pamplona course in 1 minute and 46 seconds – just four seconds quicker than the fastest ever encierro and only about 30 seconds quicker than an average one. This means that even if you were the only runner on the streets, you’d have to be a world-class sprinter to complete the course alongside or just in front of the bulls, which is why no-one even attempts to do so.

Instead, you pick a specific stretch and try to run as close to the bulls as possible, for as long as possible, as they pass through it. The route consists of six different sections, each with its own challenges. So far, like many beginners, Rob and I have stuck to the town hall square, the encierro’s widest stretch, fenced in by

specially-placed wooden barriers on each side. In 2023, for the first time, we stuck to the routes we’d planned the night before: out of the square, turning left onto another relatively spacious street, running for a few seconds in the vicinity of the bulls as they stormed through that middle section.

This year we’re planning to tackle Calle Estafeta, the route’s most popular section. Long and narrow, with a slight incline, it offers the best chance of a run right in front of the pack. But Estafeta starts with a notorious 90-degree turn nicknamed ‘Dead Man’s Curve’, where the bulls sometimes fall and separate from the rest of the herd – and a loose, panicky, distracted bull is much more dangerous than one running with its brothers. There’s also no wooden fence to slip under if you need to escape, just boarded-up bars and shops on either side.

The danger – and difficulty – of running any part of the Pamplona course comes not just from the speed and ferocity of the bulls, but from the number of runners packed onto the narrow streets, all of them fuelled by fear and adrenaline. On average there are about 2,000 participants, which creates a problem you wouldn’t have on the quieter bull runs of Cuéllar or San Sebastian de los Reyes (both of which hold their fiestas at the end of August).Falling is almost inevitable and once one person falls, several more will trip over them, so pile-ups litter the course. Any encierro veteran will tell you that if you fall down, stay down. Under no circumstances are you supposed to get up: a human being on their knees is the ideal target for a toro bravo running at 25 kph. You’re advised instead to curl up in a foetal position and wait until someone taps you, to tell you everything’s safely hurtled past. Though the mortality rate is very low (16 fatalities since 1910), there are always minor injuries and often hospitalisations.

Four rockets explode above Pamplona’s rooftops during the encierro, to inform runners of the bulls’ progress: one when the doors of their pen have been opened, a second when all six, plus the oxen, are out on the street, and a third and fourth when they enter the bullring and corrals, respectively, to signal that the run is over. Because runners have to be on the course by half past seven, the 30-minute wait for that first one to go off, at precisely the moment when the town hall bells clang eight, becomes a vital element of the whole experience. Our memories of the runs themselves are hazy, and for me they seem to happen in total silence, even though there is constant noise from the hundreds of spectators who watch from balconies; but we always remember, with hard-edged clarity, the bells and bangs of the first two rockets – then the jumpy countdown until the herd rushes into our section. It is partly for the challenge of holding our nerve, for the drama and tension of the wait, that we keep going back.