The idea that people in medieval times believed in a flat Earth is a myth that was invented in the 1800s. See https://en.wikipedia.org/wiki/Myth_of_the_flat_Earth for more.

Galileo Galilei: https://en.wikipedia.org/wiki/Galileo_Galilei :

> Galileo's championing of Copernican heliocentrism was met with opposition

... By the most published majority, whose texts would've been used to train science LLMs at the time back then.

And that most published majority believed in the Ptolemaic model. Which as https://en.wikipedia.org/wiki/Geocentric_model#Ptolemaic_mod... says:

> Ptolemy argued that the Earth was a sphere in the center of the universe...

Note. Spherical Earth. Not flat.

But could the Greeks sail?

Did ancient (Eastern?) Jacob's Staff surveying and navigation methods account for the curvature of the earth? https://www.google.com/search?q=Did%20ancient%20(Eastern%3F)... :

- History of geodesy: https://en.wikipedia.org/wiki/History_of_geodesy

FWIU Egyptian sails are Phoenician in origin.

Ancient Greeks suspected it was spherical and had an estimated size accurate within 10%.

https://en.wikipedia.org/wiki/Eratosthenes

The criticism being directed at this comment because in fact most pre-Copernican scholarship believed the world spherical is missing the point.

This. If we (without AI, even) extrapolate from the trajectory of a baseball, we would say that it would continue towards roughly the center of the earth but it doesn't.