One thing to point out is that Columbus wasn’t challenging established thinking about the earth’s shape, but rather its size. The educated populace at the time was on the ball with the earth being a sphere.
And the critics of Columbus WERE RIGHT! He was vastly underestimating the size of the earth. If North America hadn’t existed and it had just been one big ocean, he and the expedition would have perished in the middle of nowhere. Of course, the size had been calculated before his expedition (the actual values turned out be extremely close to what had been calculated), so he should have known better. There’s a reason he had trouble getting funding for his expedition…
I’m still somewhat frustrated that our history classes taught (maybe still do, I’ve been out of high school a long time) that all the naysayers thought the earth was flat.
