Ancient Greeks have known spherical Earth since at least the 3rd century B.C. According to historian Otto E. Neugebauer, the Greeks discovered Earth is a sphere from the drastic variation in the stars’ positions & motions between Greek settlements of different latitudes.
In 205 BC, Eratosthenes successfully determined the circumference of the Earth by measuring the length of the shadow cast by a rod. He did the measurement in Alexandria and timed it to coincidence when the Sun is directly overhead Syene.
2222 years after that, some flat-Earthers tried to refute the Eratosthenes experiment. They say the experiment can be applied to the flat-Earth model.