This bronze star in the pavement marks the point from which major road distances in the whole of France are calculated and it also marks the center of the city itself. It is located near the Notre Dame. Nowadays, it is a fairly popular place and some tourists even leave coins here for good luck.
More information http://www.paris-a-nu.fr/le-point-zero-des-routes-de-france/
Coordinates 48°51'11.97" N 2°20'55.895" E