That’s incorrect. It’s “one ten-millionth of the distance from the equator to the North Pole along a great circle through Paris” (https://en.wikipedia.org/wiki/Metre). Different fraction, and much better defined (different circles of longitude may have different lengths)
> That was considered not accurate enough, so it was redefined as the length of a certain metallic bar kept in Paris.
I can’t find a reference, but I think it at least partially was a matter of practicality, not of accuracy. It’s not simple to measure that 10,000 km distance (https://en.wikipedia.org/wiki/Arc_measurement_of_Delambre_an...: The arc measurement of Delambre and Méchain was a geodetic survey carried out by Jean-Baptiste Delambre and Pierre Méchain in 1792–1798 to measure an arc section of the Paris meridian between Dunkirk and Barcelona. This arc measurement served as the basis for the original definition of the metre.)
