Gnomon of Saint-Sulpice

The Gnomon of Saint-Sulpice is a sophisticated astronomical instrument built into the floor and walls of this church to solve a precise religious problem. While it is often mistaken for a remnant of an ancient pagan temple or a mysterious landmark, it was actually commissioned in the eighteenth century to determine the exact date of Easter. Because Easter must fall on the first Sunday after the first full moon following the vernal equinox, the church needed a way to observe the sun with scientific accuracy to keep their calendar aligned with celestial reality.