Scientific investigations suggest that a collision between Earth and a celestial body may have been partially responsible for the final demise of classical civilisation and the onset of the Dark Ages.
Climate data and historical references point to there having been some sort of major world catastrophe around 534/535 AD which had the effect of massively polluting the atmosphere and creating a nuclear-style winter.
Some scientists have speculated that a huge volcanic eruption was to blame, but others are now concluding that it may have been caused not by a volcano - but by a cosmic collision between Earth and a comet or large meteor up to two-thirds of a mile in diameter.
The evidence for some sort of disaster in the mid-530s, comes from an analysis from tree-ring data - an indelible record of past climate fluctuations. Data from north America and Europe show a large and sudden slow-down in tree growth which lasted for about 15 years. As a hemisphere- wide event it is the only one known of its kind. But normal scientific tests to find a volcanic cause have so far failed to discover any trace of an eruption in the mid-530s.
'The tree-ring and historical evidence tells us clearly that there was a catastrophic event at that time. If, as now seems likely, it was not volcanic in origin, then a cosmic collision is the only other real option,' said a leading UK palaeoecologist, Professor Mike Baillie, of Queen's University, Belfast, who has just published the key tree-ring data in the British scientific journal The Holocene.
'The disaster coincided with a deepening of the Dark Ages - and appears to mark a turning point in human history,' he said. Ancient chroniclers recorded that the sun 'became dim' and 'its darkness lasted for 18 months'.
The crops failed in Italy, Mesopotamia, China, the British Isles and elsewhere - and terrible famines, plague and war broke out causing long-term economic and urban decline. In some parts of China, 70-80 per cent of the population died.
The cosmic explanation is probably the front runner - because a large volcanic eruption would normally leave an acid 'signature', detectable in ice cores obtained from deep within the Greenland ice-cap.
These cores - up to two miles long - have enabled vulcanologists to plot the volcanic history of the past 9,000 years. However no trace of any eruption for the mid-530s has been found. 'The volcanic option is the least likely explanation,' said Dr Claus Hammer, an ice core expert at Copenhagen University.
The location on Earth of any sixth-century meteor collision remains a complete mystery. If the impact was on land, the crater should have come to light, although - especially if now flooded - it could well have been misidentified as of volcanic origin. There are also numerous meteor craters around the world's land surface - and not all have so far been firmly dated. The most impressive - Meteor Crater in Arizona - was formed tens of thousands of years ago. Other possible impact sites would include shallow water on continental shelves, and the Antarctic.
According to astrophysicists, a solid-rock meteor capable of causing a worldwide dust veil of the intensity described by the chroniclers, would have had to have been up to two-thirds of a mile in diameter, while a comet fragment would have needed to be one to two miles across.
The celestial body, whatever it was, would have collided with Earth at a speed of at least 10 miles a second - producing an explosion of several hundred thousand megatons (equal to more than one million Hiroshima bombs).
The crop failures, caused by the atmospheric dust veil and the consequent dimming of the sun and climatic disaster, appear in turn to have had large-scale social and political repercussions.
In the Middle East and Europe famine and poverty in the 530s seem to have been a factor in the emergence and spread of the first known great outbreak of bubonic plague in the early-540s. In Constantinople, 45 per cent of the half-million population died from the disease, which spread rapidly throughout the Middle East and Europe and re-emerged many times.
Constantinople's population shrank from around 500,000 in 520 AD to 25,000 by 650 AD.
In China, the mid-530s catastrophe coincides exactly with one of Chinese history's most mysterious events - the total desertion of the Chinese imperial capital Loyang in 534 AD, when the emperor inexplicably ordered its half- million citizens to abandon the metropolis.
This was followed by the political collapse of northern China in 535-545 after 150 years of stability and by an unexplained descent into economic and social chaos by southern China in the 540s after 200 years of economic progress.
(Photograph omitted)Reuse content