That Wikipedia page can be edited by any visitor, therefore it is not a reliable authority on the posted information. Take a look at the revision history page for your link, https://en.wikipedia.org/w/index.php?title=Myth_of_the_flat_.... Half of the edits appear not to be attributed to people but to unnamed ip addresses.

i.e. Don't believe everything you read.

To illustrate this point, go to different Wikipedia page that shows the opposite of what you wrote, https://en.wikipedia.org/wiki/Flat_Earth and look at the Early Middle Ages of Europe, https://en.wikipedia.org/wiki/Flat_Earth#Europe:_Early_Middl....