Final answer:
The ancient Greeks knew that the Earth is round through various observations and logical reasoning.
Step-by-step explanation:
The ancient Greeks were aware that the Earth is round through various observations and logical reasoning. One of the earliest pieces of evidence comes from the philosopher Pythagoras, who lived around 500 BCE. He noticed that when ships sail away, they gradually disappear from the bottom up, indicating that the Earth curves. Another Greek philosopher, Aristotle, also provided evidence of the Earth's roundness. He observed that during lunar eclipses, the Earth casts a round shadow on the Moon. Additionally, Greek mathematician and astronomer Eratosthenes accurately calculated the Earth's circumference by measuring the angle of the Sun's rays at different locations.
Learn more about Greeks' knowledge of the Earth's roundness