Having been featured in the Da Vinci Code book, St Sulpice has had to draw lines between fact and fiction; this polite notice on display in the church when I visited.
“…contrary to fanciful allegations in a recent best-selling novel, this [the line in the floor] is not a 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. … Please also note that the letters ‘P’ and ‘S’ in the small round windows at both ends of the transept refer to Peter and Sulpice, the patron saints of the church, and not an imaginary ‘Priory of Sion’…”