The metric system was created in France 1799. The goal was to create a measurement system for all people in all ages. Length unit in the metric system is one meter (from the Greek metron, meaning measure).
The length of the meter was set at a ten millionth of the distance between the North Pole and the Equator along Paris meridian. It took several years (1792-1799) to take the measurements required to produce the so-called archive meter.
Regrettably, they didn't manage to reach the exact measurements as the archive meter became 0.2 mm too short (that is why the circumference of the Earth through the poles is 40 007 863 meters). When the mistake was discovered it had passed a number of years and it was impossible to carry out a correction. Instead the meter was defined as the earlier defined archive meter's length.
In 1889, 30 new meter prototypes were produced in a platinum and iridium alloy. Then they choosed the one closes to the original archive meter in length, which in practice meant that the meters measure once again was redefined. In 1927 they managed to write down the exact definition of one meter for the first time.
Since 1983, one meter I specified with light propagation speed, the current definition of one meter will surely last for a long time:
"The meter is the length of the path travelled by light in vacuum during a time interval of 1⁄299 792 458 of a second"
For more information, visit Wikipedia.