The Eau Rouge stream itself is a 15-kilometre tributary of the Ambleve river and historically served as an administrative border under the Roman Empire and as a state border between Belgium and Prussia from 1839 to 1919. The Raidillon portion of the corner sequence was created in 1939 when the original slow uphill U-turn at the Ancienne Douane was bypassed with a faster sweeping line directly up the hill. Before 1970, the combination was narrower and tighter than the current configuration, yet cars still took it at racing speeds.
Strictly speaking, the Eau Rouge corner name refers only to the left-hander at the valley bottom. The Raidillon is the uphill sweeping blast that follows. In common usage the entire combination is referred to as Eau Rouge or Eau Rouge/Raidillon interchangeably.
Taking Raidillon de l'Eau Rouge flat out has long been one of motorsport's defining challenges. Touring cars manage the corner at 160 to 180 km/h (99 to 112 mph). Formula One cars, exploiting high downforce to generate massive cornering grip, can take it at over 300 km/h (190 mph). Fernando Alonso described the experience from the cockpit: the driver arrives downhill, encounters a sudden change of direction at the bottom, then goes steeply uphill with the exit hidden from view. As the car crests the blind summit the driver cannot immediately see where the car will land. The physical compression felt at the valley bottom is pronounced, and any mistake carries severe consequences given the subsequent long straight where time lost compounds quickly.
The corner's physical demands are compounded by its placement. A strong exit from Raidillon sets up a driver's speed through the entire Kemmel straight to Les Combes, making it a lap-time-critical section as well as a spectacle.
Several drivers have had severe accidents through the Raidillon section. Stefan Bellof died in a crash here in a Porsche sportscar. Alex Zanardi suffered a season-ending crash at the corner during a practice session for the 1993 Belgian Grand Prix in a Lotus. Jacques Villeneuve had what he described as his "best-ever crash" at the top of the Raidillon during qualifying for the 1999 Belgian Grand Prix, and his teammate Ricardo Zonta followed with a similar accident in the same weekend.
The 1994 season saw a chicane of stacked tyres installed at the Raidillon entry following the deaths of Roland Ratzenberger and Ayrton Senna at Imola, though this was removed for the following year.
The most serious modern incident occurred during the Formula 2 feature race in August 2019. Giuliano Alesi lost control climbing the Raidillon after a puncture, sending debris across the track. Anthoine Hubert, following closely, was unable to avoid the incident and crashed into the tyre barriers before being struck by the car of Juan Manuel Correa. Hubert died from his injuries and Correa suffered serious harm. The feature race was abandoned and the following day's sprint race was cancelled.
In 2021 a multi-car accident during W Series qualifying in wet conditions and a separate heavy crash by Lando Norris in Formula One qualifying — both at Raidillon — prompted widespread driver calls for immediate safety improvements. Kevin Magnussen, Pietro Fittipaldi, Jack Aitken, Zhou Guanyu, Carlos Sainz Jr., and others publicly demanded changes, supported by team principal Toto Wolff.
In October 2020 the circuit announced an 80 million euro upgrade programme. Extra run-off areas were added to the Raidillon, gravel traps were installed or expanded at Raidillon and several other corners, and a new grandstand was constructed at the top of the hill. The work was completed in March 2022. The design process evaluated twenty different configurations of the Eau Rouge section, with former Formula One drivers Thierry Boutsen and Emanuele Pirro consulted during the selection process.
Dilano van 't Hoff was fatally injured in an accident at the Raidillon in 2023, the latest incident to underscore the persistent dangers of the corner even after the 2022 modifications.
Eau Rouge/Raidillon is considered the definitive high-speed corner in circuit racing, a benchmark against which other challenging corners are measured. The 2005 Turkish Grand Prix layout included an uphill kink on the back straight that observers immediately compared to the Raidillon; it was jokingly named "Faux Rouge" — a pun combining the French word for "false" with Rouge. The corner's combination of compression, blind summit, flat-out commitment, and severe consequences for error has made it a fixture in discussions of great racing challenges, driver courage, and circuit safety for generations.