The earth is definitely not flat but it is not perfectly round, either. The radius of curvature at the equator of our planet is shorter than at the poles, although that is a relatively recent discovery. The idea that the earth was round reportedly was propounded in some circles as long ago as 500 B.C. In the 1600's A.D. Sir Isaac Newton suggested that the earth is not exactly spherical but somewhat flattened at its poles. In the 18th and 19th centuries the question of how much the earth flattens at its poles came into focus. But how to measure that, because there was no GPS. Enter the Russian astronomer and geodesist* Friedrich Georg Wilhelm Struve (1793-1864). He decided to take this on as a project and the Struve Geodetic Arc in Hammerfest, Norway commemorates his work.
*Geodesy is the science of the figure and the size of planet earth; a Geodesist is a practitioner of that science.