Eratosthenes of Cyrene (c.276 BC-c.195 BC) was a Greek mathematician, geographer, poet, astronomer, and music theorist.
He was the first person to calculate the circumference of the earth by using a measuring system using stades, or the length of stadiums during that time period (with remarkable accuracy). He was the first to calculate the tilt of the Earth’s axis (also with remarkable accuracy). He may also have accurately calculated the distance from the earth to the sun and invented the leap day. He also created the first map of the world incorporating parallels and meridians within his cartographic depictions based on the available geographical knowledge of the era. In addition, Eratosthenes was the founder of scientific chronology; he endeavoured to fix the dates of the chief literary and political events from the conquest of Troy.
He was obviously a brilliant man and a diligent thinker. His work also demonstrates the false history that many of us learned in school of people being afraid to fall off the edge of the earth and Christopher Columbus as the brave explorer who fought against the status quo of a flat Earth. Constant retelling of false history does not make a fact.