It was.

Nobody educated thought the Earth was flat. But Christopher Columbus miscalculated the size of the Earth, and everyone else correctly calculated it.

There was no way that Columbus's ships could cover a distance equal to the width of the Atlantic + the width of the Pacific + the width of North America. They would've all starved to death before they reached their actual goal: the islands east of Asia (or Asia proper).

It wasn't a calculated risk to find new land, they were trying to go to existing land and Columbus was just convinced that it was much, much, much closer than it actually was. Despite the fact that pretty close estimates of the size of the world had been calculated for a long time before him.

> But Christopher Columbus miscalculated the size of the Earth, and everyone else correctly calculated it.

There's a difference between being wrong and being irrational.

Yeah. He was both.

The earth was flat according to many people.

This isn't true. It was well-understood from antiquity that Earth was round--had to be, otherwise stuff like Eratosthenes's measuring of Earth wouldn't...well...work. It's a trivial thing to observe, too: if you're high enough over the ground, you can see horizon curvature. That knowledge was not, contrary to popular thought, widely lost during the Middle Ages even in Europe and definitely not in the Eastern Roman Empire or places east.

Serious flat-Earth thought was ideologically motivated in the late 19th and early 20th century and bears some interesting parallels to climate change denialism.

>This isn't true. It was well-understood from antiquity that Earth was round...

Among educated people able to afford and read a copy of Eratosthenes yes, but there were probably a lot of ordinary people that were not literate and were never exposed to any actual evidence to the contrary，who believed it was flat.

Flat earthers in the modern world really do have no excuse, education in the basic geometry and simple tools they need to prove it themselves is near universal in the Western world, but back then it was perhaps more understandable

>Among educated people able to afford and read a copy of Eratosthenes

who were the ones capable of funding the project in the first place

Education in basic sciences and simple tools are all people need to prove that the creation myths in <religious text> are not true, but that doesn't stop the vast bulk of humanity from subscribing to those stories.

It still exists among right-wing conspiranoids determined to believe that absolutely everything is a lie.

Not really, certainly not those who sailed ships.

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

It still is!