In fourteen-hundred and ninety-two, Columbus sailed the ocean blue—and discovered that the Earth, despite the beliefs of the Catholic Church and Spanish royalty—was round. Right? Absolutely. Not. People—ancient and medieval—have known the Earth is spherical
Game of Thrones' dark and cynical interpretation of the Middle Ages is a huge problem. The creators argue that it's a more-realistic version of the Middle Ages, but just because it's edgy, doesn't mean it's real.
George R.R. Martin wants to have his cake and eat it too: he claims his breakout hit fantasy series is based on real history, but hand-waves away criticism of his approach to issues of race. Part XXXV in Race, Racism and the Middle Ages, by Shiloh Carroll.