Early Greek philosophers such as Pythagoras (6th century BCE) and Aristotle (4th century BCE) proposed that the Earth might be spherical. However, it was not until the 3rd century BCE that the Greek astronomer Aristarchus of Samos provided the first mathematical calculation of the Earth's size and distance from the Sun.
Aristarchus's model of a heliocentric universe, with the Earth and other planets orbiting the Sun, was not widely accepted at the time. It was not until the 16th century that the Polish astronomer Nicolaus Copernicus revived the heliocentric model and provided further mathematical support for it in his book "On the Revolutions of the Heavenly Spheres."
The work of Copernicus, along with the observations and calculations of astronomers such as Galileo Galilei and Johannes Kepler, helped to establish the modern understanding of the Earth as a planet orbiting the Sun.
So, while there is no single person who can be credited with discovering that the Earth is not flat, it was through the collective efforts and contributions of many scientists over centuries that this understanding was achieved.
