The reverse is actually true, the flat-earth psyop is modern. Basically for the past 3 millennia, everyone believed that the earth was round, until some Puritans in some commune in the 1800s decided to misinterpret the bible and declare that the earth was flat. Nowhere in the actual bible does it say that the earth is flat, even Genesis is rather vague about what shape the earth is, but it describes the sky as a dome, meaning that the ancients would have at least believed the outer atmosphere was round.