Le germanopratin-alaureat

The church of Saint-Sulpice houses a white marble obelisk that stands 18 meters high and is located on the meridian of Paris. What is its purpose?
a) Nothing, it is purely decorative
b) It determines the date of the Spring Equinox or c) It pays homage to Saint Sulpice, the patron of fertility in women.

Answer: b)
The obelisk is used to determine the dates of Easter and the Spring Equinox with the copper rod encrusted in the ground. The English watchmaker, Sully, built this astronomical sundial in 1743.