The Mont Blanc massif (; ) is a mountain range in the Alps, located mostly in France and Italy, but also straddling Switzerland at its northeastern end. It contains eleven major independent summits, each over in height. It is named after Mont Blanc (), the highest point in western Europe and the European Union. Because of its considerable overall altitude, a large proportion of the massif is covered by glaciers, which include the Mer de Glace and the Miage Glacierthe longest glaciers in France and Italy, respectively. The massif forms a watershed between the vast catchments of the rivers Rhône and Po, and a tripoint between France, Italy and Switzerland; it also marks the border between two climate regions by separating the northern and western Alps from the southern Alps. The mountains of the massif consist mostly of granite and gneiss rocks and at high altitudes the vegetation is an arctic-alpine flora. The valleys that delimit the massif were used as communication routes by the Romans until they left around the 5th century AD. The region remained of some military importance through to the mid-20th century. A peasant farming economy operated within these valleys for many centuries until the glaciers and mountains were "discovered" by the outside world in the 18th century. Word of these impressive sights began to spread, and Mont Blanc was first climbed in 1786, marking the start of the sport of mountaineering. The region is now a major tourist destination, drawing in over sixmillion visitors per year. It provides a wide range of opportunities for outdoor recreation and activities such as sight-seeing, hiking, rock climbing, mountaineering and skiing. Around one hundred people a year die across its mountains and, occasionally, bodies have been lost and entombed in its glaciers for decades. Access into the mountains is facilitated by cable cars, mountain railways and mountain huts which offer overnight refuge to climbers and skiers. The long-distance Tour du Mont Blanc hiking trail circumnavigates the whole massif in an 11-day trek of . The Mont Blanc Tunnel connects the French town of Chamonix on the northern side with the Italian town of Courmayeur in the south. The high mountains have provided many opportunities for scientific research, including neutrino measurements within the tunnel and impact of climate change on its highest slopes. Recent rises in average temperatures have led to significant glacial retreat across the massif and an awareness