The Santerno river rises in the hills south-west of Imola. It winds its way down for 50 kilometres until it reaches the town, which is home to over 68,000 people and to a racing circuit: the Autodromo Enzo e Dino Ferrari. In April 1994 two men who had raced at the circuit many times before looked down at the river from the first of the track’s 15 corners: Tamburello. They had been testing their cars at the track, rounding the corner at over 300kph (186mph), and had become concerned about the concrete wall which separated the circuit from the river.

Ayrton Senna at Imola

One of the men had crashed at the corner five years earlier. His car exploded into flames, but men with fire extinguishers quickly arrived at the scene and saved his life. His companion pointed towards the Santerno. “Look,” he said, “we can’t move the wall, there’s a river behind it”. The two men agreed there was nothing that could be done about the wall. And with that Gerhard Berger and Ayrton Senna walked away. Tamburello is an innocuous enough word in Italian: it means ‘tambourine’, and is also the name of a court game similar to squash.

But to the Formula One world Tamburello is like Terlamenbocht at Zolder where Gilles Villeneuve died, or the nameless stretch of the Hockenheimring which claimed Jim Clark. It is the place where one of the greatest of them all met an untimely, unthinkable end. The Imola circuit had been in use for four decades and by the time it held its first world championship race in 1980 a chicane had been inserted before the start/finish line to reduce the speed of the cars as they approached Tamburello. But the constant improvements in car design had their inevitable effect and by 1994 drivers were tackling the corner at close to maximum speed without a hint of a lift on the throttle as their cars screamed towards the Tosa hairpin.

It was uncommon to see anyone struggle in the corner unless they were unlucky enough to suffer a technical failure there. When that happened, the consequences were often fearful. In 1987 a suspected tyre failure sent Nelson Piquet’s Williams into the Tamburello wall, leaving him with concussion and forcing him to miss the race. Then came Berger’s crash in 1989, caused by front wing failure. Two years later the same happened to Michele Alboreto, who was hospitalised with broken ribs and a deep gash. In 1992 a second Williams driver, Riccardo Patrese, was taken to hospital after crashing at the corner during testing – again a tyre failure was to blame.

The subject of safety had been a growing concern of Senna’s for several years. He had befriended Professor Sid Watkins, taken an interest in his work and had a heart-to-heart talk with him following Ratzenberger’s death. At the drivers’ meeting, held at 11 o’clock on the morning of the race, Berger led the drivers in raising a complaint about the use of a course car to lead the field on the formation lap at the previous race.  He did so at Senna’s urging, as both believed the car was too slow and prevented drivers from being able to get their tyres up to temperature. The decision was taken not to use the course car for the formation lap.

Before leaving the drivers observed a minute’s silence in memory of Ratzenberger. Some of the more experienced drivers had witnessed fatalities before – including Martin Brundle, Michele Alboreto and Andrea de Cesaris. Senna himself had competed in a support race at Zolder in 1982 on the same weekend Gilles Villeneuve was killed. For many others the shock hit them all the harder for being unfamiliar. While increasingly concerned with safety matters, Senna’s impulse to compete spurred him on, and that side of his life presented him with further challenges. He had agonised over his switch from McLaren to Williams at the beginning of the year, and was still acclimatising to his new environment.

Against expectations Williams had begun the season on the back foot. The FW16 handled nervously, and while Senna had tamed its knife-edge handling to claim three pole positions in a row, he went into the third race of the season pointless. He’d spun out in Brazil and been eliminated at the first corner in Japan – and on both occasions he’d been running second to Michael Schumacher. Designer Adrian Newey produced a heavily revised FW16 for Imola. The front wing was raised, its wheelbase shortened and the cockpit reshaped to reduce buffeting.

Out on the track, Senna had another spin in the car. He returned to the garage and debriefed race engineer David Brown with the words no one in the team wanted to hear: “It’s worse…”

In contrast Schumacher arrived in Italy with 20 points on the board. Benetton had ironed out many of their problems with their B194 which they had started testing a month earlier than Williams, and seemed to have sussed the new variable of refuelling far better than Williams. Still Senna suspected there was more to it than that. Watching Schumacher’s Benetton in action in Japan he had become convinced the car was using an illegal traction control system. Ahead of the race, Williams stationed commercial manager Richard West on the roof of their garage to film Schumacher’s start in a bid to gather evidence.

Almost unnoticed amid the dire events of the previous day, JJ Lehto had made an encouraging return to racing in his first event of the year after being injured in testing. He qualified his Benetton on the third row of the grid, within a second of team mate Schumacher. The crowd was pleased to find both of their beloved Ferraris within the first three rows. The V12-engined cars were quickest of all through the Tosa speed trap, hitting 334kph (208mph), and had achieved their best combined qualifying performance of the year so far. The carnage of the preceding days left a single car each from Jordan, Simtek and Pacific on the grid, belonging to De Cesaris, David Brabham and Bertrand Gachot respectively.

While Williams’ covert cameraman was focused on the back of one Benetton as the race started, the other failed to move at all. Car after car missed JJ Lehto but Pedro Lamy was not so fortunate. The Lotus driver had started 17 places further back and didn’t see the Benetton until he pulled out to pass De Cesaris. His car slammed into the Benetton and an explosion of shrapnel burst into the air. Some of it cleared the debris barrier and nine spectators were injured, one seriously.

While wrecked cars were cleared away the Safety Car was summoned. This came as a surprise to most onlookers – the Safety Car was still novel in F1 20 years ago, the idea having been borrowed from IndyCar racing not long previously. And start-line accidents such as this one had normally prompted a stoppage of the race so the track could be cleared of debris. Max Angelelli was at the wheel of the Opel Vectra which now headed the field, and the Italian Formula Three champion was driving close to the limit of the car’s abilities. But he was doing one lap in the time it took F1 cars to do two, and Senna drew alongside in a vain attempt to urge the car to move faster. Angelelli headed for the pits at the end of the fifth lap. Senna’s race engineer David Brown told him the Safety Car was coming in and he radioed back an acknowledgement. It was the last the team heard from him.

Senna had said in a pre-race interview he didn’t enjoy how the reintroduction of refuelling that year had turned races into a series of sprints. Previously drivers had to manage heavy fuel loads in the early stages of the race, preserving their cars while their handling gradually improved. Senna led at the restart and Schumacher gave chase. The Benetton driver was scheduled to pit three times and so his car would have been lighter than Senna’s, which was due to make two stops. Rounding Tamburello once more at full speed Senna hugged the inside of the corner, a stream of sparks flying from the rear of his car, the largest plume appearing as he left the third dark patch of resurfaced tarmac in the middle of the corner.

It was on that same patch of tarmac where, one lap later, Senna’s Williams inexplicably snapped out of control. Theories of varying credibility for what happened in this moment abound, but what is known was that Senna was trying to regain control of the car until the moment of impact. While millions of people around the world witnessed what happened next, Schumacher had the clearest view of what unfolded at Tamburello on lap seven.

“I saw that Senna’s car was already touching [the ground] quite a lot at the back on the lap before,” he said after the race. “The car was very nervous in this corner, and he nearly lost it.”

“On the next lap he did lose it. The car touched with the skids, went a bit sideways, and he just lost it.”

Senna had enough time to get onto the brakes and reduce his speed to 217kph (135mph). Drivers had survived accidents at higher speeds – it was Senna’s misfortune to be struck by a flying piece of suspension which inflicted a fatal head injury. That much was clear to Professor Sid Watkins when he arrived at the scene. Just hours earlier he had suggested his friend walk away from the sport, telling him “I don’t think the risk is worth continuing”. The race was stopped and the medical helicopter landed next to the crash scene, waiting to carry Senna away as it had done for Ratzenberger 24 hours earlier.

Amid the chaos and confusion Erik Comas, who had pitted on the first lap, was accidentally released from the pits and came around Tamburello at speed, braking to a stop as he reached the crash scene. He parked his Larrousse facing the helicopter, and could see the medical team working on Sennas’s grievously wounded body. Two years earlier Senna had come to his aid when Comas had crashed at Spa-Francorchamps. Now he felt powerless to help the man he felt had helped save his life. Comas eventually returned to the pits and took no further part in the race. As was the case following Ratzenberger’s crash, those watching on television were spared none of the horror. The intrusive and upsetting coverage of the dying minutes of the sport’s most famous driver, appalled and transfixed 200 million viewers worldwide.

Those in the UK watching the race on the BBC were spared the graphic coverage of the accident aftermath. By sheer chance the British broadcaster had chosen the race to bring their own camera to film material in the pit lane for the first time, and so were able to supply alternative footage. Eventually Senna was put in the helicopter and flown to Maggiore hospital in Bologna. And now, to the surprise of some, the race would continue. Before the deaths of 1994 Bernie Ecclestone had said a race would be resumed in the event of another fatal accident. Now the contingency plan was being enacted, just as it had after Ricardo Paletti’s death 12 years earlier.

Ecclestone had arrived in race control to impose some order on a chaotic scene. He was given an update on Senna’s conditions from Watkins via the FIA’s press delegate Martin Whitaker, which Ecclestone passed on to Senna’s brother Leonardo. But somewhere along the line Watkins’ report that Senna’s injuries were to his ‘head’ was confused with the word ‘dead’.

Understandably distraught, Leonardo’s grief multiplied as Ecclestone’s original report was corrected, and he was further upset when he learned the race would resume. In the Benetton hospitality suite, a weeping Schumacher initially told his manager Willi Weber he did not want to race any more. But when the call to resume the race was given, all the drivers bar Comas returned to the grid. In the Benetton hospitality suite, a weeping Schumacher initially told his manager Willi Weber he did not want to race any more. The cars headed around the track on another formation lap. Twice they passed the places where their comrades had fallen – the scarred wall where Ratzenberger had crashed, the bloodstained ground where Senna’s car came to a stop.

If anyone at Williams was still paying attention to how good Schumacher’s starts were, they would have seen him get beaten off the line by Berger, whose V12 out-gunned the Benetton’s Ford V8 on the long drag to Tosa. While waiting for the restart, Berger noticed he had incurred heavy damage to his front suspension after striking a piece of debris from the Senna crash. It was repaired in time for the restart and he led the first 11 laps. Of all the drivers on the grid, Berger had the closest connections to Senna, his friend and former McLaren team mate, and to Ratzenberger, his fellow Austrian. This understandably weighed heavily on his mind, and when his car’s handling began to deteriorate due to a broken rear shock absorber he pitted from the lead and retired.

Like Brabham, Hill bravely chose to continue despite his team mate’s serious and unexplained accident. Williams had seen Senna’s broken steering column lying next to the car and took the precaution of disabling the power steering system on Hill’s car. He also made a good start and lunged down the inside of Schumacher at Tosa on the first lap. The pair made contact and Hill slipped back with a broken front wing which was remedied in the pits soon afterwards. As the cars could not be topped up with fuel on the grid, Schumacher arrived in the pits for his first of three scheduled refuelling stops just a few laps later. Berger retired soon after and that handed the lead of the race to Mika Hakkinen, for the first time in his career.

It was only ever going to be a temporary situation before Schumacher strode past on his way to a third consecutive victory. But it was joyless triumph, and on this dark day for the sport Nicola Larini also had no cause for cheer despite taking second place, achieving his first podium finish – and the last to date for an Italian in a Ferrari. In a weekend which had delivered one nasty shock after another, the final trauma occurred on the 44th lap of the combined two-part race. Michele Alboreto, who had not been on the grid for the original start, was accelerating from his pit box when the right-rear wheel separated from his Minardi.

As there was no pit lane speed limit at the time the wheel hurtled from the car, striking three Ferrari mechanics and one from Lotus, before bouncing across the track where it was fortunately not collected by another driver. Shortly afterwards the sole Jordan of de Cesaris became the last retirement of the race when he crashed at the exit of Tosa. Brabham had already parked his Simtek after feeling a problem develop in his steering. Christian Fittipaldi lost a likely points finish after a brake failure on his Arrows four laps from home. That allowed Hill to claim the final point after recovering from his troubled restart.

The result was decided on an aggregate of the first five laps prior to Senna’s crash and the subsequent 53-lap race, which further added to the confusion. Schumacher, Larini and Hakkinen attended a sombre podium ceremony. During the race news filtered through about the seriousness of Senna’s condition. But it wasn’t until 6:40pm that the organisers confirmed the staggering news that he had succumbed to his injuries.

An earthquake had struck the motorsport world, and the tremors were soon felt far beyond the perimeter of the Autodromo Enzo e Dino Ferrari. Jackie Stewart and son Paul gathered around a television monitor at Silverstone where their F3 team was competing. Not far away at the Rye House kart circuit at Hoddesdon, nine-year-old Lewis Hamiltoncried when his father told him his hero was dead. Across the Atlantic in Michigan Emerson Fittipaldi, Brazil’s first world champion, was called in from a test to be given the dreadful news about his countryman. The shattered remains of Senna’s FW16 was sealed in the garage. Marshals had recovered a small Austrian flag from the cockpit, which Senna had hoped to wave in memory of Ratzenberger after the race.

Fatalities in motor racing did not end with the deaths of Ayrton Senna and Roland Ratzenberger at Imola 24 years ago. But this was the moment which prompted the sport to proactively seek new areas for safety improvement, instead of waiting for the next tragedy to point out where improvements needed to be made. Seventeen years later Berger reflected on his fateful conversation with Senna in an interview with Maurice Hamilton. “Instead of looking at the bigger picture and thinking about adding a chicane, we were just thinking how we could move the wall,” he said.

“I remember we talked about this at the exact place where Ayrton died. I think about this a lot.”

In the days that followed Imola Formula One came under unparalleled media scrutiny. The deaths of Senna and Ratzenberger headed news bulletins and filled front pages worldwide. The inevitable questions of why the crashes happened and how the fatalities could have been prevented eventually forced the sport to take drastic measures. But as the teams departed Imola there was only deep, numbing shock as they left behind two of the drivers who had gone there with them.