I got sucked into the Wikipedia rabbit hole and ended up reading about the history of the Roman Coliseum. It seemed that many in Rome didn't know what is was used for and basically used it as a quarry to build other buildings. Considering many Romans didn't even know what the Coliseum was, I was wondering how much of Europe knew about the Roman Empire during the Dark and Middle Ages.
Also, a good answer to a virtually identical question: https://www.reddit.com/r/AskHistorians/comments/41llbl/where_medieval_europeans_aware_that_the_roman/