The meridien line materialized by a brass inlay in
the pavement of this church is part of a scientific
instrument built here during the 18th century. This
was done in full agreement with Church authorities
by the astronomers in charge of the newly-
established Paris Observatory. They used it for
defining various parameters of the earth's orbit.
Similar arrangements have been made, for the sake of
convenience, in other large churches like the
Bologna Cathedral where Pope Gregory XIII had
preparatory studies made for the enactment of the
present Gregorian calendar.

Contrary to fanciful allegations in a recent best-
selling novel, this is not a vestige of pagan temple.
No such temple ever existed in this place. It was
never called a "Rose-Line". It does not coincide with
the meridien 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.

Please also note that the "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, not an imaginary "Priory of Scion".

http://www.stsulpice.com/