In 1861, Whymper successfully completed the ascent of Mont Pelvoux, the first of a series of expeditions that threw much needed light on the topography of an area which at the time was very poorly mapped. From the summit of Mont Pelvoux, Whymper discovered that it was overtopped by a neighbouring peak, subsequently named the Barre des Écrins, which, before the annexation of Savoy added Mont Blanc to the possessions of France, was the highest point in the French Alps. Whymper climbed the Barre des Écrins in 1864 with Horace Walker, A. W. Moore and guides Christian Almer senior and junior.