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Origin and history

The geodetic steles of Sausheim and Oberhergheim, located in the Upper Rhine (Great East), were raised in August 1804 under Napoleon I by astronomer Maurice Henry (1763–25). Their aim was to measure a base of 19,045 km between the two sites, known as the Ensisheim base, to establish a topographic map of Switzerland then under French domination. This distance, the longest ever measured at the time, served as a reference for geodetic triangulation calculations.

The steles, inspired by Egypt's post-campaign Egypt (1798–1801), take the shape of the pink sandstone obelisks of the Vosges, 5 to 7 meters high, surrounded by twelve pillars. The one in Oberhergheim bears a commemorative inscription specifying its role in mapping the Helvetia and determining the figure of the Earth. Originally, a Bonaparte effigy shield adorned the Sausheim stele, destroyed by the Austrians during the invasion of 1813.

Classified as Historical Monuments in 1979, these steles symbolize the scientific appropriation of the territory by Napoleonic France. Their design also reflects the technical advances of the time, mixing geodesy, astronomy and imperial ambition. The Sausheim stele was restored in 1985, while that of Oberhergheim retains its original state, a material witness to this cartographic enterprise.

The initial project included a third stele at Jungholtz-Thierenbach and a different location for Sausheim (Rixheim Hill), modified due to atmospheric refractive effects. These adjustments illustrate the technical challenges faced by 19th-century geodesians, combining mathematical precision with environmental constraints.

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