Comment by nearbuy

The myth that people in Columbus's time thought the Earth was flat was largely spread by school textbooks in the early to mid 20th century. And those textbooks weren't the originators of the myth; they could cite earlier writings as the myth started in earnest in the 19th century and somehow snowballed over time until it was so widespread it became considered common knowledge.

Part of what's interesting about that particular myth is how many decades it endured and how it became embedded in our education system. I feel like today myths get noticed faster.