Created by Louis XIV, this observatory is the oldest in the world, the four sides of which are oriented towards the cardinal points. Inside, the Paris Meridian, which passes through the Cassini room on a north-south axis, is marked on the floor by a brass strip. This line was established during the summer solstice of 1667 on the site of the observatory, but was abandoned in favour of the Greenwich line in 1884. The observatory is responsible for determining Coordinated Universal Time (UTC).