Which is the highest mountain in the Alps?

Mont Blanc, at around 4,808 metres - and the figure changes, because the summit is a dome of ice whose depth varies. It is resurveyed every two years and has ranged over several metres in recent decades, so the mountain's official height is a measurement of snow as much as rock.

Its ownership is genuinely unresolved. France and Italy have never agreed where the border runs across the summit; French maps place it entirely in France, Italian maps run the line through it, and the dispute traces to differently worded treaties from 1861 and a Napoleonic-era map. It is largely amicable and periodically flares over rescue jurisdiction and tunnel access.

Mountaineering as a sport began here. The first ascent in 1786, by Jacques Balmat and Michel Paccard, was made for a prize offered by a Genevan scientist who wanted the summit reached so its altitude could be measured - so the sport started as a paid scientific errand. It is now climbed by thousands a year, and enough of them are unprepared that the mayor of Chamonix has required a deposit toward rescue and funeral costs, and the melting permafrost that used to hold the rock together is making the standard route measurably more dangerous.