The original Spa-Francorchamps circuit was essentially a speed course, with drivers managing higher average speeds than on other race tracks. At the time, the Belgians took pride in having a very fast circuit, and to improve average speeds, in 1939 the former slow uphill U-turn at the bottom of the Eau Rouge creek valley, called the Ancienne Douane (until 1920, there was a German Empire customs office here), was cut short with a faster sweep straight up the hill, called the Raidillon. At Eau Rouge, southbound traffic was allowed to use the famous uphill corner, while the opposite downhill traffic had to use the old road and U-turn behind the grandstands, rejoining the race track at the bottom of Eau Rouge.