Odd/ironic fact: people didn't believe the Earth was flat back then. That's a modern confusion. They believed the Sun revolved around the Earth. Wikipedia has a whole article dedicated to this common belief:
"The earliest clear documentation of the idea of a spherical Earth comes from the ancient Greeks (5th century BC). The belief was widespread in the Greek world when Eratosthenes calculated the circumference of Earth around 240 BC. This knowledge spread with Greek influence such that during the Early Middle Ages (~600–1000 AD), most European and Middle Eastern scholars espoused Earth's sphericity.[3] Belief in a flat Earth among educated Europeans was almost nonexistent from the Late Middle Ages onward ... Historian Jeffrey Burton Russell says the flat-Earth error flourished most between 1870 and 1920, and had to do with the ideological setting created by struggles over biological evolution"
I asked ChatGPT the same question and it prevaricated:
"There is evidence that some people in medieval times believed the Earth was flat, while others believed it was round. The idea that the Earth is round, or more accurately, an oblate spheroid, has been around since ancient times. The ancient Greeks, for example, knew that the Earth was a sphere. However, the idea that the Earth is flat also has a long history and can be traced back to ancient civilizations as well. During the Middle Ages, the idea that the Earth was round was not widely accepted, and there was significant debate about the shape of the Earth. Some people continued to believe in the idea that the Earth was flat, while others argued for a round Earth. It is important to note that the medieval period was a time of great intellectual and scientific change, and ideas about the shape of the Earth and other scientific concepts were still being developed and debated."
But from what I know, it's wrong, at least as far as we know the historical record (of course there may have been peasants who believed otherwise but their views weren't recorded). The fact that the Earth is a sphere is obvious to anyone who watched a ship sail over the horizon, which is an experience people had from ancient times.
https://en.wikipedia.org/wiki/Myth_of_the_flat_Earth
"The earliest clear documentation of the idea of a spherical Earth comes from the ancient Greeks (5th century BC). The belief was widespread in the Greek world when Eratosthenes calculated the circumference of Earth around 240 BC. This knowledge spread with Greek influence such that during the Early Middle Ages (~600–1000 AD), most European and Middle Eastern scholars espoused Earth's sphericity.[3] Belief in a flat Earth among educated Europeans was almost nonexistent from the Late Middle Ages onward ... Historian Jeffrey Burton Russell says the flat-Earth error flourished most between 1870 and 1920, and had to do with the ideological setting created by struggles over biological evolution"
I asked ChatGPT the same question and it prevaricated:
"There is evidence that some people in medieval times believed the Earth was flat, while others believed it was round. The idea that the Earth is round, or more accurately, an oblate spheroid, has been around since ancient times. The ancient Greeks, for example, knew that the Earth was a sphere. However, the idea that the Earth is flat also has a long history and can be traced back to ancient civilizations as well. During the Middle Ages, the idea that the Earth was round was not widely accepted, and there was significant debate about the shape of the Earth. Some people continued to believe in the idea that the Earth was flat, while others argued for a round Earth. It is important to note that the medieval period was a time of great intellectual and scientific change, and ideas about the shape of the Earth and other scientific concepts were still being developed and debated."
But from what I know, it's wrong, at least as far as we know the historical record (of course there may have been peasants who believed otherwise but their views weren't recorded). The fact that the Earth is a sphere is obvious to anyone who watched a ship sail over the horizon, which is an experience people had from ancient times.