The French Revolution didn’t just shake up the government of France, but its systems of mathematics as well. One of the radical changes was in the measuring of distance, and you can still find one of the first standard meters installed in its original place in Paris.
The “mètre étalon” is a small shelf of marble installed beneath the arcade at 36, rue Vaugirard, right across from the Senate at the Palais du Luxembourg. It’s one of 16 that were installed after, on March 26, 1791, the Académie des Sciences defined the meter for the first time. The only other to survive is at 13, de la Place Vendôme, although unlike the Vaugirard meter it’s been moved from its original location.
Up to then under royal rule the country had used all manner of arbitrary measurements to define distance, so this highly scientific new standard had to be conveyed in a physical way. The Paris meters, installed between February of 1796 and December of 1797 in busy street areas, also gave people something with which to copy and confirm their own meters.
To define the meter, French astronomers Delambre and Méchain measured 10 millionths of the distance from the North Pole to the Equator through a Paris meridian, which you can still find at the center of the Paris Observatory.