The Raidillon did not exist in the circuit's original configuration. Until 1939, drivers navigating the old Spa layout had to negotiate the Ancienne Douane, a slow uphill U-turn at the top of the Eau Rouge valley. That year, the hairpin was replaced by a faster sweeping connection straight up the hill — the Raidillon — which eliminated the hairpin entirely and raised average lap speeds considerably. The name derives from the French word for a short, steep rise.
The Eau Rouge stream itself, which crosses beneath the track at the valley bottom, gave the original left-hand turn at the base its name. After the circuit's major 1979 reconstruction, the two elements — Eau Rouge at the bottom and Raidillon climbing away — were retained on the shortened 6.947 km permanent layout and combined into a single challenging complex. In everyday usage, drivers and commentators use the two names interchangeably to refer to the whole sequence.
The combination works by launching drivers at high speed from the La Source hairpin down a short descent before the track crosses the stream and turns sharply left at Eau Rouge, immediately transitioning into the Raidillon's blind uphill right-left-right sequence. The summit is invisible from the entry, and the compression at the valley bottom loads the car heavily while demanding simultaneous steering input.
Touring cars negotiate the section at 160 to 180 km/h. Formula One cars, aided by very high downforce, pass through at speeds exceeding 300 km/h. Two-time World Champion Fernando Alonso described the sensation: drivers experience a sudden change of direction at the bottom, a steep uphill climb where the exit cannot be seen, and a compression through the body as the car reaches the crest. The section is also decisive for race pace: the Kemmel Straight follows immediately, meaning any error costs significant time while a clean exit provides a platform for overtaking at the Les Combes corner ahead.
Jacques Villeneuve noted that the nature of downforce actually requires drivers to go faster through the corner, as increasing speed generates more downforce, which in turn provides the grip to sustain the line. Taking the corner completely flat — without lifting — became a standing challenge that defined the best drivers and cars of every era.
The Raidillon has been the site of some of motorsport's most serious accidents. Stefan Bellof was killed at the section during the 1985 1000 km Spa sportscar race while driving a Porsche. Alex Zanardi suffered a season-ending crash there in practice for the 1993 Belgian Grand Prix. Jacques Villeneuve and his BAR teammate Ricardo Zonta both crashed heavily at the top of the Raidillon during qualifying for the 1999 Belgian Grand Prix, the incidents later revealed to involve a personal bet between the two drivers to attempt the corner completely flat.
The 2021 season produced a cluster of high-profile incidents. During W Series qualifying, a rain-triggered chain collision involving six cars, including Sarah Moore, Abbie Eaton, Beitske Visser, Ayla Agren, and Belen Garcia, resulted in multiple cars airborne in the Raidillon run-off. The following day, Lando Norris aquaplaned his McLaren into the barrier during Formula One qualifying. Both incidents prompted a sustained public campaign from drivers across multiple series demanding immediate safety modifications.
The most tragic incident occurred during the 2019 Formula 2 feature race. French driver Anthoine Hubert died after a multi-car incident triggered when Giuliano Alesi's car shed debris at the Raidillon crest, setting off a sequence of events that brought Hubert's car into the path of Juan Manuel Correa at high speed on the Kemmel Straight. Juan Manuel Correa sustained severe leg injuries. The race was abandoned and its sprint companion event cancelled.
Following years of debate about the run-off geometry at the Raidillon — specifically a tendency for impacting barriers to deflect cars back into the racing line rather than absorb them — the circuit announced a major renovation in October 2020, part of an 80 million euro upgrade also intended to allow motorcycle racing at Spa for the first time.
Work was completed in March 2022. The changes included an expanded run-off area at the Raidillon, repositioned gravel traps, and modifications to the tyre barriers. Twenty different iterations of the Eau Rouge section were evaluated before the final design was selected, with input from former Formula One drivers Thierry Boutsen and Emanuele Pirro alongside simulation data. A new grandstand was constructed at the top of the hill. The 2022 revision also marginally shortened the overall circuit to 6.985 km as a consequence of track geometry adjustments for motorcycle safety.
The Raidillon de l'Eau Rouge is consistently cited by drivers, engineers, and commentators as one of the defining tests in world motorsport. Its combination of speed, blind commitment, and physical loading has produced some of the sport's most memorable moments of both brilliance and tragedy. The corner's appearance in sim racing titles, broadcast graphics, and motorsport imagery has made it one of the most recognised pieces of tarmac in the world, a landmark that connects the historic road circuit era of Spa with the permanent modern track.