Jacek Yerka; Fantasia;
Fallacious ideas and beliefs are documented and widespread;
Christopher Columbus's efforts to obtain support for his voyages were never hampered by a European belief that Earth was flat.
Sailors and navigators of the time knew that Earth was spherical. Though they, correctly, disagreed with Columbus's estimates of the distance to India, which was approximately one-sixth of the actual distance.
If the Americas did not exist, and had Columbus continued to India, he would have run out of supplies before reaching it at the rate he was traveling.
Without the ability to determine longitude at sea, he could not have noticed that his estimate was in error in time to return. This longitude problem remained unsolved until the 18th century, when the lunar distance method emerged in parallel with efforts by inventor John Harrison to create the first marine chronometers.
The intellectual class had known that the Earth was spherical since the works of the Greek philosophers Plato and Aristotle. Eratosthenes made a very good estimate of the Earth's diameter in the third century BC.