Église Saint-Sulpice, Paris

Église Saint-Sulpice is a Catholic parish church whose name honours Sulpice the Pious. Its construction began in 1646, and several architects shaped the building, including Louis Le Vau, Daniel Gittard, Gilles-Marie Oppenord, and Giovanni Niccolò Servandoni. The church belongs to the baroque tradition and is protected as a historic monument.

The most unexpected feature is the astronomical instrument inside. A narrow brass strip crosses the transept floor, continues up a white marble obelisk, and receives a sunbeam entering through a small opening in a high window. This is a gnomon: the bright spot shifts with the seasons, reaching the obelisk during winter.

Jean-Baptiste Languet de Gergy commissioned it in the eighteenth century to help establish the date of Easter. Pierre Charles Le Monnier later used the line for long-term solar observations, measuring the gradual change in Earth’s axial tilt. Despite a famous fictional claim, this line is not Paris’s meridian; that passes a few hundred metres east through the Observatory.

The church also contains murals by Eugène Delacroix. Look for the inlaid line crossing the floor and meeting the obelisk: here, sunlight turns the church into a precision instrument.