St.Gildas reports that the object that came through the sky in his day went into the Western Sea ~ we'd say it probably went over the horizon ~ but he didn't realize the world was round.
A group in Australia say they've found two offshore craters created in 535 AD by what they believe to have been a comet.
On a more serious matter I suspect some of the prophecies in Daniel and in Revelation have to do with this particular event.
I’ve read apparently firsthand accounts of a very large asteroid described as “horrible in it’s blackness” making what sounds like a glancing blow throught the upper atmosphere, in an Old English an account from the early middle ages. The sound was the most terrifying thing, according to this. No, I can’t provide a source or a link. I encountered it in the process of researching mass behavior during plague outbreaks, it was peripheral. I remember it because it was so unusual.
We’ve lived in a period of relative inactivity, speaking both geologically and astronomically. Many accounts coming down from ancient history that have been written off as somehow fantastical have factual origins in these, as do many elements of prophecy, imho.
I don’t see such prophecies as having been fulfilled, though.