I think it’s one of the most common historical misconceptions. It seems like whenever the topic of “things school taught you that was wrong” comes up online, atleast one person will say that their teacher told them that Colombus discovered the earth wasn’t flat. How did this misconception start?
Check this answer from /u/Georgy_K_Zhukov
https://www.reddit.com/r/AskHistorians/comments/6c6asf/when_and_why_did_the_myth_develop_that_the/