Lots of different accounts, artifacts, and buildings remain from “the dark ages”. Historians go over all of this and come to a conclusion about things that have taken place. Just because Rome wasn’t in power doesn’t mean that Europe was a complete shitstorm. Mass manipulation was not really feasible at the time, since there was no large central government over the whole of Europe. If anything, it might be more reasonable to ask why we believe anything written by the romans, since they had the power to manipulate records across Europe.
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