Disasters are always looming. Most likely it was a raid or invasion of some kind. Mankind's history is a long series of disasters from the four horsemen: Famine, Pestilence, War, and Plague.
In "Lessons from Jupiter" (Southern Sky magazine, January/February 1995), Clube and David Asher wrote :
"Calculations based on an orbit related to that of P/Encke reveal intersections with the Earth's orbit around AD 600 and before that AD 400, so that a swarm would have been near the Earth's orbit for a duration of a few centuries around that epoch, the time of the European Dark Age. This then is a critical extended period when we might well expect several multi megaton [explosive] events, indeed a great many if we consider the globe as a whole. The perspective is evidently one in which we expect the Roman Empire to have gone into decline owing to multiple-Tunguska bombardment causing great tracts of land to be deserted and whole communities or nations to be suddenly dislocated. Of necessity, the period becomes one of barbaric movements." Chinese historical records of AD 540 say : "Dragons fought in the pond of the K'uh o. They went westward....In the places they passed, all the trees were broken. " The calculations for the Taurids suggest that we pass through the core of the meteor stream approximately every 2,500 years - today, we are passing through the outer edges. The last two occasions when we passed through the core were in 2200 - 2000 BC and in AD 400 - 600. The epoch around AD 3000 looks like being a fun time too - the Y2K doomsayers can always say they just got the millennium wrong. In 1983, the orbiting IRAS infra-red satellite discovered cometary "trails" (not tails), representing debris along the path of various short-period comets. These trails consist of debris, most of which would be microscopic in size, but how many large objects are there in the trails? If there are many large objects in these trails, then Duncan Steel notes in his above-mentioned book :"