The Great Aletsch Glacier is the largest and longest glacier in the Alps in terms of area. It is located on the southern slope of the Bernese Alps in the Swiss canton of Valais. The length of the glacier is 22.6 km, and the area is given as 78.49 km². The Aletsch Glacier drains into the Rhone via the Massa. The area of the entire catchment area of the Massa is 195 km², of which around two thirds were glaciated in 1973. The Upper and Middle Aletsch Glaciers are often included in the area figures, as they were previously connected to the Great Aletsch Glacier. The total glaciated area including these glaciers was around 128 km² in 1973, and an area of 163 km² is assumed for 1863.