The International Border in Lake Geneva: Hard to See, but Very Real

Until the early 16th century, Lake Geneva was almost entirely part of the Duchy of Savoy. In 1536, Bernese conquests in the Pays de Vaud and those by Valais in the Chablais completely reshaped the situation. These conquests, formalized by the treaties of Lausanne in 1564 and Thonon in 1569, created a long international border within the lake. With the entry of the cantons of Geneva and Valais into the Swiss Confederation in 1815, and the annexation of Savoy to France in 1860, Lake Geneva became a Franco-Swiss space. Since recognizing a lake border—by definition intangible—is not as straightforward as recognizing a naturally dividing or densely marked land border, we will now review the stages of its establishment.

In 1536, Bern occupied the Pays de Vaud, the Geneva surroundings, and the southern part of the lake up to Thonon. Meanwhile, the people of Valais invaded the Chablais and also advanced as far as Thonon. Thus, the lake became “Swiss” in the sense that its shores were occupied by Bern and two allied Swiss Confederation states (Valais and Geneva). In the second half of the 16th century, supported by Spain, the Duke of Savoy made efforts to reclaim all or part of his possessions in Savoy. With Bern, negotiations resulted in the Treaty of Lausanne in 1564, in which Bern kept the Pays de Vaud but withdrew from the southern part of Lake Geneva and the Geneva surroundings. Valais withdrew as far as St-Gingolph but retained the territory now known as the Valaisan Chablais.

Article 20 of the 1564 Treaty of Lausanne stipulates that the middle of the lake would serve as the border between Bern and Savoy. From then on, geographic maps marked this border, such as the one by Thomas Schöpf in 1578. The use of the lake's midpoint as the border was reaffirmed in 1815 when the new canton of Geneva received Savoyard and French lands to make its territory more cohesive and connected to Switzerland. The Treaty of Turin on March 16, 1816, between the Kingdom of Sardinia and Geneva confirmed that the boundary between the neighboring sovereignties lies “in the middle of the width” of the lake.

The annexation of Savoy to France in 1860 did not immediately alter the situation. It wasn't until the 20th century that the Swiss and French states sought to simplify the border's layout. Indeed, while the concept of the lake’s midpoint is easy to understand in everyday language, its practical application in a lake environment is complicated. Besides the impossibility of placing durable physical markers in water, determining a median delimitation line requires numerous measurements.

The convention between Switzerland and France on determining the border in Lake Geneva, dated February 25, 1953, laid the foundation for the demarcation we still know today. It recognized that the theoretical median line is constructed from “the centers of circles inscribed between the Swiss and French shores.” However, for simplification, “a six-sided polygonal line that balances the areas” replaced it. Two transverse extensions at Hermance and St-Gingolph complete the boundary line. Thus, using the coordinates of the seven points, the international border line is easily drawn. Today, thanks to geolocation on maps from the Federal Office of Topography (Swisstopo), anyone can follow the international border by boat. The Valais-Vaud border extends in a straight line from the middle of the Rhône to the Franco-Swiss point off the coast of Saint-Gingolph. The same applies to the Vaud-Geneva border off Hermance.

Sources

• Treaty of Lausanne, October 30, 1564 [AEB Fach Savoyen]
• Maps by Thomas Schöpf, 1578 [UB Bern, MUE Ryh 3211: 8]
• Treaty of Turin, March 16, 1816 [AEG Savoie 37]
• Convention between Switzerland and France on determining the border in Lake Geneva, February 25, 1953 [AFS K1#3226]
• Decision of the Federal Assembly, December 23, 1953 [BBl 1953 III 71]