Crypte Archéologique, stretching 118 meters under the Parvis du Notre Dame, was built by the city of Paris in order to house the archeological finds discovered during the excavation undertaken in 1965 by the Direction des Antiquites historiques de I'Ile de France and the Commission du Vieux Paris. It contains ruins of Roman quaysides, ramparts and hypocausts, medieval cellars, shops and pavements, the foundations of the Eglise Ste-Geneviève-des-Ardens, an 18th-century foundling hospital and a 19th-century sewer. Imbedded in the surface of the plaza itself are brass strips which locate the streets and buildings that were removed.
As far back as 507, this site was chosen by King Clovis – the first Frankish Merovingian King – for a basilica to serve as a tomb for him and his wife Clothilde. In 512 Sainte-Geneviève, patroness of Paris was buried here (then moved to a new St Geneviève just down behind the Pantheon). The site sits at the top of a hill overlooking the Latin quarter.
King Louis XV vowed in 1744 that if he recovered from his illness he would replace the ruined church of the Abbey of St Genevieve with an edifice worthy of the patron saint of Paris. He did recover, and entrusted Abel-François Poisson, marquis de Marigny with the fulfillment of his vow. In 1755, Marigny commissioned Jacques-Germain Soufflot to design the church, with construction beginning two years later. He had the intention of combining the lightness and brightness of the gothic cathedral with classical principles, but its role as a mausoleum required the great Gothic windows to be blocked. There are 3 domes, allowing the visitor to look through the inner oculus to the painting above. The effect of the dome is spectacular. In antiquity, one could barely see any of the dome when approaching from the outside, it was obscured by the porch and the intermediate block, so it was a surprise when one entered the rotunda. Ones eyes are carried up toward the oculus, which lets in enough light to make the whole area seem light and airy. The coffers give the effect of producing a magnitude of lights and darks in the dome, constantly changing as the beam of light and its projected circle from the oculus move with the sun. This gives one the impression that the building is dynamic and not solid and weighty, but light, airy, and uplifting, like the sky outside on a clear day. The dome seems to expand as one looks at it.