You’ve heard of the final mile. This is the final metre.
Up until 1791 they’d been measuring things without any care for a standard, much like the USA today, but then the French astronomers Delambre and Méchain measured 10 millionths of the distance from the North Pole to the Equator through a Paris meridian, and then the government of the day installed 16 demonstrator metres around the city.
This is the last one in its original installation. There’s one other that’s been moved so who even knows if it’s legit ¯_(ツ)_/¯