The climb of Alpe d'Huez has become one of the more noted mountain stages. During the 2004 Tour de France it was the scene of a mountain time trial on the 16th stage. Riders complained of abusive spectators who threatened their progress up the climb. On this stage it is not uncommon for a low end estimate of the spectators in attendance to number 300,000. During a famous head to head battle between Anquetil and Raymond Poulidor on Puy de Dôme it was estimated that at least a half a million people were on hand. Mont Ventoux is often claimed to be the hardest in the Tour because of the harsh conditions. Another notable mountain stage frequently featured climbs the Col du Tourmalet, the most visited mountain in the history of the Tour. Col du Galibier is the most visited mountain in the Alps. The 2011 Tour de France stage to Galibier marked the 100th anniversary of the mountain in the Tour and also boasted the highest finish altitude ever: . Some mountain stages have become memorable because of the weather. An example is a stage in 1996 Tour de France from Val-d'Isère to Sestriere. A snowstorm at the start area led to a shortening of the stage from to just . During the 2019 Tour de France multiple landslides and hail storms forced two critical mountain stages to be considerably shortened. Authorities made every effort to plow the road and make the course safe, but the volume of hail, mud and debris proved too much.