Saint Sulpice, a famous Gothic Church in Paris, France was first built in 1645 and it became completed in 1746. It is a very famous landmark as it was dedicated to Saint Sulpicius, who was the bishop of Broughes in the 7th century; a trying time of tyrannical persecution and political upheavals.
The church has witnessed notorious baptisms and burials as one of the center stage churches in France. However, the importance of this location to the novel is that two salient symbols, the Obelisk next to Saint Peter, as well as the gnomon, a strange, brass meridian line that was once part of astronomical instrument built on site. It is quite unique. Together these odd objects seemingly lead "somewhere" as if in a code.
In The Da Vinci Code, St. Sulpice is supposed to be the holder of the keystone that would lead to the location of the Holy Grail. Partly mythical and partly eccentric, it is no question why Dan Brown would have selected it as a setting.
The Church of Saint-Sulpice, it is said, has the most eccentric history of any building in Paris. Built over the ruins of an ancient temple to the Egyptian goddess Isis, the church possesses an architectural footprint matching that of Notre Dame to within inches. The sanctuary has played host to the baptisms of the Marquis de Sade and Baudelaire, as well as the marriage of Victor Hugo. The attached seminary has a well-documented history of unorthodoxy and was once the clandestine meeting hall for numerous secret societies.
Whether the church actually served these purposes is completely left for speculation. Certainly the church would seem like the ideal place,complete with catacombs, naves, and the mystery of the objects. However the church issued a memorandum stating the veracity behind the ideas presented in The Da Vinci Code, particularly the idea that during the Winter equinox the moonlight beams on the obelisk and irradiates a message. In the novel, the reason why this happens is because St. Sulpice was supposedly built over the ruins of an ancient Pagan temple. This is untrue.
Contrary to fanciful allegations in a recent bestselling novel, this is not the vestige of a pagan temple. No such temple ever existed in this place. It was never called a "Rose Line." It does not coincide with the meridian traced through the middle of the Paris Observatory which serves as a reference for maps where longitudes are measured in degrees East or West of Paris. No mystical notion can be derived from this instrument of astronomy except to acknowledge that God the Creator is the master of time.
So, basically contrary to the fantastic origin of the church presented by Dan Brown in The Da Vinci Code, the reality is that it is a Gothic structure whose location made it part of the central lives of famous and not-so famous Parisians. However, its aesthetics render it a place worthy of a legendary and fantastic background.