Geodesic stele à Sausheim dans le Haut-Rhin

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Origin and history

Sausheim's geodetic stele is a topographical sight erected in August 1804 under the reign of Napoleon I, as part of the mapping of Switzerland then under French domination. It is part of a set of two steles, with that of Oberhergheim, distant from 19,045 km, forming the base of Ensisheim. This distance, measured accurately, served as a reference for geodetic triangulation, constituting at the time the longest base ever measured on Earth. The stele, originally planned on Rixheim Hill, was finally installed in Sausheim due to the technical constraints of atmospheric refraction.

Designed by the team of astronomer Maurice Henry, the stele takes the form of a pink sandstone obelisk of the Vosges, part of the egyptomanian current that followed the Egyptian campaign (1798–1801). Originally, she wore a Bonaparte effigy shield, destroyed by the Austrians during the invasion of 1813. Surrounded by twelve pillars arranged in a circle, it symbolizes both a scientific tool and a Napoleonic engineering memorial.

Classified as historical monuments by order of 5 December 1979, the Sausheim stele was restored in 1985. His inscription, which has now disappeared on the model of Oberhergheim, recalled his role in determining the figure of the Earth and the map of the Helvetia. These steles illustrate the scientific ambition of the First Empire, combining territorial conquests and technical progress, while marking the Alsatian landscape of a unique geodetic heritage.

The precise coordinates of the stele (47° 47′ 26,5246′′ N, 7° 23′ 14,9417′′ E) lie along departmental road 201, near Mulhouse and Colmar. Its location, chosen for its visibility and geological stability, makes it a material witness to the methods of measuring the nineteenth century, now accessible to the public.

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