The Greeks knew the Earth is spherical. For example, Pythagoras (570-495 BCE), Aristotle (384-322 BCE), and Euclid (circa 450 BCE) wrote about the Earth as a sphere. Eratosthenes (276-194 BCE) even calculated the circumference of the Earth to within 1%. He also wrote about the idea that India could be reached by sailing westward from Spain.
Nearly 2,000 years later during the time Columbus sailed the ocean blue, most religious nuts believed the Earth was flat and he would fall off. What happened to truth? Although many educated people knew all along, the dogma of the brainwashed religious nuts over the centuries suppressed and terrorized the masses into believing things like the Earth is flat, the Earth is only a few thousand years old, women are property, and other such nonsense. The harm caused by formal religions over the eons is incalculable.