There was a book I read in my school’s library when I was 8 or so on the Bermuda triangle that claimed (or at least implied?) that a roman ship was sunk there.

Though the book was for children and presumably completely unreliable, I have seen it written before, so maybe that’s where they saw it too?

I bought all the DLC back when they released, but despite playing hundred of hours since I only completed Dawnguard a couple of years ago and have never touched Dragonborn