Who owns the summit of Mont Blanc? The Franco-Italian border in question

Two official answers coexist, and no body has arbitrated between them. For France, the summit lies entirely within its territory, between the communes of Saint-Gervais-les-Bains and Chamonix-Mont-Blanc. For Italy, the border runs over the summit itself, which is therefore shared and falls half within the commune of Courmayeur, in the Aosta Valley. Both states rely on the same nineteenth-century treaties and draw different lines from them: the contradiction is cartographic and legal, and has never been resolved by a joint decision.

The Treaty of Turin signed on 24 March 1860 attaches Savoy and the County of Nice to France, but describes no precise line in the high mountains. Its Article 3 merely refers the question to a body yet to be created: "A joint commission will determine, in a spirit of equity, the borders of the two states, taking into account the configuration of the mountains and the necessity of defence." This is where all the later ambiguity lies. The founding text does not say where the border runs at Mont Blanc; it says who will have to say so, and by which criteria. These two criteria, the configuration of the terrain and the defensive imperative, do not necessarily point to the same line.

The delimitation convention signed in Turin on 7 March 1861 repeats the wording of the earlier protocol: the new border follows the limit that then separated the Duchy of Savoy from Piedmont. It gives no detail at the summit. The boundary-marking minutes of 26 September 1862, ratified by both governments, complete the work: the commissioners look for the important passes where markers should be placed, thirteen in all, and note that the border follows a course from summit to summit. Neither the convention nor the minutes mark out the high mountains, which by nature cannot be marked. Everything therefore rests on the maps annexed to them, drawn at 1/50,000. On these maps, the line is traced at a scale where a few tenths of a millimetre equal several tens of metres on the ground. Italian readers see a line passing over the summit; French readers see a line passing below it, several tens to several hundred metres lower.

The current French line first appears on the General Staff map drawn up in 1865 by Captain Jean-Joseph Mieulet, cartographer of the French army, who had climbed Mont Blanc on 14 July 1863 to survey the massif. His map makes the border skirt the summit glaciers to the south and places the summit entirely in French territory, where the maps annexed to the treaties followed the ridge. The result is a strip of land claimed by France and regarded as Italian by Italy: the triangle extending from the summit to Mont Blanc de Courmayeur (4,748 m), taking in the Rocher de la Tournette (4,677 m). It is this triangle, and not the summit alone, that forms the material object of the disagreement.

Each national institute reproduces its own state's reading, without telling the reader that another exists. The IGN follows the Mieulet line: summit and Col Major French, Mont Blanc de Courmayeur shown as a border summit. The Istituto Geografico Militare strictly follows the watershed: summit shared, Mont Blanc de Courmayeur entirely Italian. The most revealing contrast comes from a third party: Switzerland long reproduced the French version on its maps, before swisstopo switched in 2018 to a hatched display signalling a status of disputed territory. It is the only one of the three official cartographies to explicitly acknowledge the dispute.

On the French side, the communal division derives from a prefectural order of Haute-Savoie dated 21 September 1946, which divides the area of the Dôme du Goûter and Mont Blanc between Saint-Gervais-les-Bains, Chamonix-Mont-Blanc and Les Houches. This order adopts the interpretation placing the summit entirely in France and divides it between Saint-Gervais and Chamonix, the boundary between the two communes following the Goûter and Bosses ridge. A little-known consequence: Saint-Gervais-les-Bains ends up holding an exclave on the glaciated southern slope of the summit cap, a scrap of territory detached from the rest of the commune. The local urban plan adopted by Saint-Gervais in 2016 itself acknowledges that this exclave lies on the Italian side of the border as delimited in 1860. On the Italian side, the summit belongs to Courmayeur, in the Aosta Valley.

A joint Franco-Italian delimitation commission has met since 20 April 1988 in Nice. At its meeting of 24 March 1995 in Paris, it notes that the disagreement over Mont Blanc exceeds its technical remit and must go up to the foreign affairs ministries. In July 1995, the Italian authorities forward a memorandum setting out their reading; at the meeting of 6 June 1996 in Sanremo, France acknowledges that a difference of interpretation exists. The document exchange that follows says everything about the state of the file: since the French copies of the 1860 annexed maps disappeared during the German occupation, it is Italy that supplies a certified true copy of the treaty annex, with France sending back a 1930 photograph of the lost documents. No agreement has been signed since.

On the summit ridge, the question is invisible: no marker, no sign, no check, no entry or exit formality. A rope team climbing by the Goûter route and crossing into Italy passes nothing physical. The disagreement becomes concrete as soon as an authority has to be designated. Rescue falls to two distinct public services, the PGHM on the French side and the Aosta Valley alpine rescue on the Italian side, whose competence is determined by the state on whose territory the accident occurs: at the summit itself, that determination depends on which map is adopted. The same logic applies to administrative police: a mayor's police power stops at the limits of their commune, so a municipal order from Saint-Gervais-les-Bains applies to the summit cap only under the French reading. In practice, cross-border cooperation handles real cases without waiting for the law; but the climber who wants to know which regulations apply at the summit has, to this day, no single answer.