Harbinger of Doom?
This article suggests that there might have been some factual basis to the ancient myths of comets as Harbinger's of doom. It seems that it's possible a hunk of Halley's comet hit the Earth in 536 A.D., triggering a 10 year bout of cold and famine.
The ancients had ample reason to view comets as harbingers of doom, it would appear.
A piece of the famous Halley's comet likely slammed into Earth in A.D. 536, blasting so much dust into the atmosphere that the planet cooled considerably, a new study suggests. This dramatic climate shift is linked to drought and famine around the world, which may have made humanity more susceptible to "Justinian's plague" in A.D. 541-542 — the first recorded emergence of the Black Death in Europe.
The new results come from an analysis of Greenland ice that was laid down between A.D. 533 and 540. The ice cores record large amounts of atmospheric dust during this seven-year period, not all of it originating on Earth.
More detail in the link.