Here is an example of the myth of the dark ages. In the first pages of Thomas Aquinas’ masterpiece, the Summa Theologia, Thomas is arguing that theology is a real way of knowledge alongside philosophy. He points out that some truths can be known in multiple ways, and for an illustration he uses the roundness of the earth: “For the astronomer and the physicist both may prove the same conclusion: that the earth, for instance, is round: the astronomer by means of mathematics (i.e. abstracting from matter), but the physicist by means of matter itself.” It’s a throwaway illustration for Thomas, which he thinks will be persuasive because it’s not controversial.
Students are often shocked to find this example staring at them from their thirteenth-century book: That everybody knows the earth is round. They try to reconcile that fact with the myth of the dark ages, according to which medievals thought the earth was flat and in 1492 Columbus defied conventional wisdom by sailing right around it without falling off the edge. “Maybe they forgot between 1274 and 1492.” Maybe. Or maybe the flat earth is part of the myth of the dark ages, devised to keep you from looking into the middle ages lest you find powerful allies there.
Read the whole thing, which isn't primarily about the Myth of the Dark Ages but about the Christian tradition we should be glad to claim a part of in the thousand years between Augustine and Luther.