The terrain and the hot weather mean an exhausting day for the 168 riders who took the start from Pau in southwest France for a 206.5-kilometer (128.3-mile) trek into the mountains.
Surprise leader Cyril Dessel wore the yellow jersey, the first Frenchman since 2004 to do so, according to the AP.
Tour de France riders were in the Pyrenees on Wednesday, but there were only two agonizing climbs in the mountains that straddle the border with Spain.
The 11th stage runs into the hardest challenge first - an 18.5-kilometer ascent up Tourmalet pass, which is ranked "hors categorie," or beyond classification. After three more climbs, riders scale the long, less steep Puerto de Beret up to the finish in Pla-de-Beret, Spain.
The head of the Voronezh region, Alexander Gusev, confirmed the death of Major General Vladimir Zavadsky.