Which Greek thinker calculated the circumference of the earth accurately?

Eratosthenes is renowned for his remarkable calculation of the Earth's circumference around 240 BCE. He used a clever method that involved comparing the angle of the sun’s rays at noon in two different locations in Egypt—Alexandria and Syene (now Aswan). By measuring the angle difference and knowing the distance between the two cities, he applied geometry to estimate the Earth's circumference. His calculation was remarkably close to modern measurements, demonstrating not only his mathematical skills but also his understanding of the Earth as a spherical body.

This accomplishment puts Eratosthenes among the early pioneers of geography and science, showcasing the advanced thinking of ancient Greek scholars. His work laid the foundation for later measurements of the Earth and established him as an important figure in the history of science.