The distance from the North Pole to the Equator via Paris was originally defined as 10,000 km. Then it [the metre] was based on a standard pole, then on the wavelength of a particular type of light.
Those who are old enough to have learned Imperial units at school will be delighted to discover that the metre was at one time defined in terms of the rod, pole or perch.
The rod or perch or pole is a surveyors tool and unit of length equal to 5 1⁄2 yards, 16 1⁄2 feet, 1⁄320 of a statute mile or one-fourth of a surveyor's chain. The rod is useful as a unit of length because whole number multiples of it can equal one acre of square measure.