On lap 35 of the 1955 Le Mans 24-Hour race, the #20 Mercedes-Benz 300 SLR of Pierre Levegh and John Fitch struck the back of the slower moving Austin-Healey 100 S of Lance Macklin and Les Leston.
The #6 Jaguar D-Type driven by eventual winner of the race, Mike Hawthorn (and which can be at 1:19 of this video), slowed down suddenly because Hawthorn saw a pit board advising him to take on fuel. Macklin in the Austin-Healey also slowed down to avoid Hawthorn but Levegh in the Mercedes-Benz who had seen none of this, did not slow down at all and ran into the back of Macklin's car at more than 150mph.
The Mercedes-Benz swerved left and dug into the ground and began to destroy itself as pieces from the wreckage continued to hurtle through the spectators; killing 83 and injuring a further 120. Pierre Levegh also died at the scene of the accident but somehow Lance Macklin survived and would go on to live until the age of 82.
In the weeks that followed Pierre Levegh was savaged by the French media for causing the accident. This was probably the safest option as he could not defend himself - he was dead.
You'd think that after the deaths of 83 people, that the organisers would have cancelled the race but they didn't. The authorities reasoned that cancelling the race would jam the roads as people left and ambulances needed to get in and out as swiftly as possible.
The race continued through the night and until the next afternoon, when 24 hours after it had begun, Mike Hawthorn and Ivor Bueb's Jaguar had covered 2572 miles to win the race.
Mercedes-Benz unsurprisingly immediately withdrew their other two entries and by the end of 1955, they formally withdrew from all factory-sponsored motorsport. They would return to Le Mans as an engine builder in 1985 for the Sauber team and to Formula One also as an engine supplier to Sauber.
In 1997 Mercedes-Benz returned to sportscar racing and to Le Mans but this was only short lived, as after a series of accident involving their cars flipping in 1999, they once again cancelled their sports car program. They would however enjoy success again though when in 2010 Mercedes-Benz returned to Formula One as a complete car builder after buying out Brawn GP. They have subsequently won both a World Drivers' and Constructors Championship.
What I find utterly staggering about the 1955 accident though, isn't the primitive crash protection for the spectators but the fact that even though cars were travelling at more than 190mph down the Mulsanne Straight, drivers did not wear seat belts because they thought that it was safer to the thrown out of a car in an accident rather than be trapped in the car if it caught fire.
Almost immediately an investigation was carried out into finding out what could be done to make motor racing safer but the response was predictably anemic. France, Spain, Germany and Switzerland placed bans on motor racing until tracks could be brought up to standard but curiously, the ban on Swiss motor racing still stands some 60 years later. Serious consideration to the design of motor racing circuits didn't really happen until about the 1970s.
Even so, with the speeds that sports cars do, there's still always the chance that this sort of thing could happen again. Motor racing remains dangerous.