The understanding that the Earth is round dates back to ancient Greek philosophers and scientists.

• Pythagoras, around 500 BC, is often credited as one of the first to propose a spherical Earth, reasoning from the round shape of the Moon

• Aristotle (384–322 BC) provided observational evidence, noting that during lunar eclipses, the Earth's shadow on the Moon is always round, which would only be possible if the Earth were spherical. He also observed that ships disappear hull-first over the horizon, supporting the idea of a curved surface

• The Greek mathematician Eratosthenes (3rd century BC) is credited with the first scientific proof of Earth's roundness by calculating its circumference with remarkable accuracy using the angles of the Sun's rays at different locations. His work laid the foundation for modern geography and astronomy

• Practical proof came much later with the Magellan-Elcano expedition (1519–1522), which was the first successful circumnavigation of the globe, conclusively demonstrating Earth's sphericity through direct experience

In summary, while the idea of a spherical Earth was proposed and supported by Greek thinkers like Pythagoras, Aristotle, and Eratosthenes, the first practical, navigational proof was provided by the Magellan-Elcano expedition in the early 16th century