Claude-Nicolas Ledoux’s “Élévation du Cimetière de la Ville de Chaux” (1804) - plan for the cemetery of the city of Chaux

Some of the buildings and objects that the famous architect Ledoux depicted were  abstract in their meaning and unbuildable in their design.  For example, in one his last sketches published in 1804 in a compilation of engravings, Ledoux portrayed a cosmology of clouds floating above the cemetery of the city of Chaux, a city which he had originally helped to plan.  A miniature representation of the Earth,  on a cloud, is surrounded by a number of smaller planetoids in orbit.  Suspended in air without support, almost seem to resemble a collection of aerostatic spheres, not unlike the famous hot-air balloon unveiled by the Montgolfier brothers in 1783.  With its geocentric model, Ledoux appears to grant the cemetery inhabitants a Ptolemaic afterlife.

source: Radical Bourgeois Architects in the Age of Reason and Revolution