Who was the first person to discover that the world isn't flat?

The idea that the Earth is round dates back to ancient Greece, with philosophers like Pythagoras and later Aristotle providing early evidence for a spherical Earth. However, it was the Greek philosopher and mathematician Eratosthenes in the 3rd century BCE who first calculated the Earth's circumference using measurements of shadows in different locations. While he may not have been the "first" in the absolute sense, his work was significant in demonstrating the Earth's roundness through empirical observation and mathematical reasoning.