Paris Observatory was funded in 1667 by king Louis XIV
The oldest building was designed by the architect Claude Perrault
It is the oldest observatory still serving. It is built without wood (to avoid fire) or metal (to avoid magnetic disturbances). It is a large rectangle (31 m x 29 m) with its four faces oriented with the cardinal points
of the compass. The latitude
of the south face defines the Paris latitude (48° 50' 11''). The meridian
line passing through its center defines the Paris longitude
The foundations are as deep (27 m) as high is the building itself. The basement is connected with the Paris catacombs
(visits forbidden). The catacombs consist of 65 km of underground galleries.