British Archaeology, no 30, December 1997: Features


Comets and disaster in the Bronze Age

Cosmic impact is gaining ground as an explanation of the collapse of civilisations, writes Benny Peiser

At some time around 2300BC, give or take a century or two, a large number of the major civilisations of the world collapsed. The Akkadian Empire in Mesopotamia, the Old Kingdom in Egypt, the Early Bronze Age societies in Israel, Anatolia and Greece, as well as the Indus Valley civilisation in India, the Hilmand civilisation in Afghanistan and the Hongshan Culture in China - the first urban civilisations in the world - all fell into ruin at more or less the same time. Why?

A thousand years later, at around 1200BC, many of the civilisations of the same regions again collapsed at about the same time. This time, disaster overtook the Myceneans of Greece, the Hittites of Anatolia, the Egyptian New Kingdom, Late Bronze Age Israel, and the Shang Dynasty of China.

The reasons for these widespread and apparently simultaneous disasters - which coincided also with changes to cultures and societies elsewhere, such as in Britain - have long been a fascinating mystery. Traditional explanations included warfare, famine, and more recently ‘systems collapse’, but the apparent absence of direct archaeological or written evidence for causes, as opposed to effects, has led many archaeologists and historians into a resigned assumption that no definite explanation can be found.

Some decades ago, the hunt for clues passed largely into the hands of natural scientists. Concentrating on the earlier set of Bronze Age collapses, researchers began to find evidence that natural causes, rather than human actions, may have been initially responsible. There began to be talk of climate change, volcanic activity, and earthquakes - and some of this material has now found its way into standard historical accounts of the period.

Agreement, however, there has never been. Some researchers favoured one type of natural cause, others another, and the problem remained that no single explanation appeared to account for all the evidence.

Over the past 15 years or so, however, a new type of ‘natural disaster’ has been much discussed and is beginning to be regarded, by many scholars, as the most probable single explanation for widespread and simultaneous cultural collapse, not only in the Bronze Age but at other times as well. The new theory has been advanced largely by astronomers, and remains almost completely unknown by archaeologists (notable exceptions include Prof Mike Baillie of Queen’s University, Belfast, and Dr Euan Mackie at Glasgow University). The new idea is that these massive cultural disasters were caused by the impact of comets or other types of cosmic debris on the Earth.

The hunt for natural causes for these human disasters began when the French archaeologist Claude Schaeffer published his book Stratigraphie Comparée et Chronologie L’Asie Occidentale in 1948. Schaeffer analysed and compared the destruction layers of more than 40 archaeological sites in the Near and Middle East, from Troy to Tepe Hissar on the Caspian Sea and from the Levant to Mesopotamia. He was the first scholar to detect that all had been totally destroyed several times in the Early, Middle and Late Bronze Age, apparently simultaneously. Since the damage did not show signs of military or other human involvement, and in any case was too excessive, he argued that repeated earthquakes might have been responsible.

At the time he published, Schaeffer was not taken seriously. Since then, however, natural scientists have found widespread and unambiguous evidence for abrupt climate change, sudden sea level changes, catastrophic inundations, widespread seismic activity and evidence for massive volcanic activity at several periods since the last Ice Age, but particularly at around 2300BC, give or take 200 years. Areas such as the Sahara, and around the Dead Sea, were once farmed but became deserts. Tree rings show disastrous growth conditions at c 2350BC, while sediment cores from lakes and rivers in Europe and Africa show a catastrophic drop in water levels. In Mesopotamia, vast areas of land appear to have been devastated, inundated, or totally burned.

Scholars who, following Schaeffer, favour earthquakes as the principal cause of civilisation collapse argue that the world can expect vast earthquakes every 1,000-2,000 years, leading to widespread abandonment of sites; while scholars who prefer climate change as the principal cause argue that severe droughts caused agriculture to fail and that societies inexorably fell apart as a result.

Yet what was the cause of these earthquakes, eruptions, tidal waves, fire-blasts and climate changes? By the late 1970s, British astronomers Victor Clube and Bill Napier of Oxford University had begun to investigate cometary impact as the ultimate cause. Then in 1980, the Nobel prize-winning chemist Luis Alvarez and his colleagues published their famous paper in Science that argued that a cosmic impact had led to the extinction of the dinosaurs. He showed that large amounts of the element iridium present in geological layers dating from about 65 million BC had a cosmic origin.

Alvarez’s paper had an immense influence and stimulated further research by such British astronomers as Clube and Napier, Prof Mark Bailey of the Armagh Observatory, Duncan Steel of Spaceguard Australia, and Britain’s best-known astronomer Sir Fred Hoyle. All now support the theory of cometary impact and loosely form what is now known as the British School of Coherent Catastrophism.

These scholars envisage trains of cometary debris which repeatedly encounter the Earth. We know that tiny particles of cosmic material penetrate the atmosphere every day, but their impact is insignificant. Occasionally, however, cosmic debris measuring between one and several hundred metres in diameter strike the Earth and these can have catastrophic effects on our ecological system, through multi-megaton explosions of fireballs which destroy natural and cultural features on the surface of the Earth by means of tidal-wave floods (if the debris lands in the sea), fire-blasts and seismic damage.

Depending on their physical properties, asteroids or comets that punctuate the atmosphere can either strike the Earth’s surface, or explode in the air. Those that strike leave an impact crater, such as the well-known Baringer Crater in Arizona caused by an asteroid made of iron some 50,000 years ago. At least ten impact craters are known around the world dating from after the last Ice Age, and no fewer than seven of these date from around the 3rd millennium BC - although none occurred in the Near East.

Air-explosions, however, can be more disastrous. A recent example - known as the Tunguska Event - occurred in 1908 over Siberia, when a bolide made of stone exploded about 5km above ground and completely devastated an area of some 2,000 km2 through fireball blasts. The bolide, although thought to have measured only 60m across, had an impact energy of about 40 megatons, three times as great as the Arizona example and equivalent to the explosion of about 2,000 Hiroshima-size nuclear bombs - even though there was no actual physical impact on the Earth. (The object that destroyed the dinosaurs, by contrast, is thought to have had a diameter of about 10km.) A smaller cometary blast occurred over the Brazilian rainforest in 1930.

In addition to the physical impact of comets, the British astronomers point to the occasional massive influx of cosmic dust high above the stratosphere which can cause a dramatic drop of global temperatures, leading to the suspension of agriculture; and also to the massive influx of cosmic chemicals (associated with dust) with, as yet, incalculable biochemical potentials. Until recently, the astronomical mainstream was highly critical of Clube and Napier’s ‘giant comet’ hypothesis. However, the crash of the comet Shoemaker-Levy 9 on Jupiter in 1994 has led to a change of attitudes. The comet, watched by the world’s observatories, was seen to split into 22 pieces and slam into different parts of the planet over a period of several days. A similar impact on Earth, it hardly needs saying, would have been devastating.

According to current knowledge, Tunguska-like impacts occur every 100 years or so. It is, therefore, not far-fetched to hypothesise that a super-Tunguska may occur every 2,000, 3,000 or 5,000 years and would be capable of triggering ecological crises on a continental or even global scale. In the past, sceptics have demanded the evidence of a crater before they would accept an argument of cosmic impact, but it is now becoming understood that no crater is necessary for disastrous consequences to ensue. The difficulty this leaves scholarship, however, is that in a Tunguska Event no direct evidence is left behind. It may be impossible to prove that one ever took place in the distant past.

The extent to which past cometary impacts were responsible for civilisation collapse, cultural change, even the development of religion, must remain a hypothesis. But in view of the astronomical, geological and archaeological evidence, this ‘giant comet’ hypothesis should no longer be dismissed by archaeologists out of hand.

Dr Benny J Peiser is a historian and anthropologist at Liverpool John Moores University. With Mark Bailey and Trevor Palmer, he is editing Natural Catastrophes during Bronze Age Civilisations (BAR, 1998, in preparation).


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Change and evolution in Roman Britain

How much did Britain really change under the Romans? Debbie Day reports

In AD43, an invading Roman army landed in south-eastern Britain and heralded four centuries of Roman rule. But how much did Britain, and the British landscape, really change under the Romans?

The traditional view was that the Romans brought a completely new way of life - in short, civilisation - to a society that was still essentially barbarous. More recently that view has been questioned, and whether Britain experienced ‘change or continuity’ is now one of the most vigorously debated issues in Roman studies.

Unfortunately, some reseachers have become entrenched in one or other extreme position, whereas in reality Britain of course experienced both change and continuity in the Roman period.

Continuity is sometimes mistakenly regarded as meaning ‘staying the same’; but it means a continuous sequence or logical progression, which implies some alteration of the original state. Change, on the other hand, is not necessarily sudden and dramatic, but can take effect over a long period of time. While these definitions bring change and continuity closer together, they also make them more difficult to tell apart. For example, a farmstead at which there was activity over a number of centuries probably represents continuity, but what about an Iron Age farmstead which evolved into a large villa? Looking, for this article, only at Wessex in the first two centuries AD, it is apparent from numerous sites that changes were taking place.

One of the first consequences of the Roman invasion was the construction of a comprehensive system of roads, built by the army within a generation or two of their arrival. Engineered, using a sophisticated surveying system, with gravel surfaces and bridges where necessary, the new road network represented a far-reaching modification to the landscape. Prior to the arrival of the Romans, there were no engineered roads in Britain - only trackways which followed the natural routes across the countryside. In some places the Roman roads followed these ancient routes, but frequently they took a more direct course. It was the establishment of the road system which truly enabled the growth of most of the other Roman features in the landscape.

Another significant innovation was the establishment of regularly-planned towns. Hillforts, which served many purposes in Iron Age society, were largely abandoned, and their functions were taken over by new urban settlements, situated closer to water sources and the new road system. New building materials and Roman architectural styles were employed in the construction of shops, public buildings, and large private homes.

Rural settlement patterns also changed in some areas, most notably in the development of the villa estate system. Most villas did not reach their greatest extent until the later Roman period, but there are a number known in Wessex from soon after the invasion.

The face of religion in the Wessex landscape was altered, as the architecture of sacred sites changed dramatically. In many cases, new gods were worshipped alongside the old. With a few exceptions temples were Romano-Celtic rather than truly classical in style, and the cults practised in Britain were idiosyncratic, but they were deeply influenced by the religions of Rome nonetheless. Also affected were burial practices, and there was a general shift towards cremation.

Significant changes also occurred in the industrial landscape, including the establishment of a major lead mining operation in the Mendips, a natural resource which was hardly used by the pre-Roman peoples of Wessex. The levels of production in many existing industries increased dramatically, such as pottery. Innovations such as the potter’s wheel also came into use on a large scale at this time. In the construction industry, bricks, tiles, shale and stone began to be used in addition to wattle and daub and timber.

As trade expanded and a monetary system based on low denomination coinage became established, new jobs were created, and prestige goods previously only available to elites became more widely accessible. The role slavery played in the development of the landscape is uncertain, but farmers in the early Roman period started producing a winter as well as a summer wheat crop, which had the effect of allowing a great increase in the amount of livestock kept year-round.

As elsewhere in the Empire, owning property was the most desirable form of investment, and farms and villa estates were run to produce a surplus and profit. A number of improved farming tools and techniques were introduced, including a better plough which could cut through heavier soils, and made it possible to increase field sizes.

Many researchers believe that a number of new, or at least improved, plant varieties were introduced by the Romans, including rye, oats, vetch, and flax, as well as cabbage, parsnip, turnip, carrots and other vegetables, fruit trees such as the vine, plum, apple, mulberry, and walnut, and flowers such as the rose, violet, lily, pansy and poppy.

Cultural changes are difficult to trace from archaeology, and are particularly hard to measure in diet, lifestyle, and individual beliefs. Did Roman dress really become widely adopted by the native British, as Tacitus states? It is known that the population was growing in this period, although exact population levels are still unclear.

Finally, there was peace. Warfare was endemic in Iron Age society, but after the fighting associated with the Conquest ended, cattle raiding, capture into slavery, and battles with neighbouring tribes were no longer a threat. This provided a stability in the region, to the benefit of the developments taking place in the landscape and society as a whole.

Continuity, on the other hand, can be found at many of the early Roman towns in Wessex. Silchester, Winchester and Chichester (which had shifted from Selsey at about this time) were all located on top of, or beside, late Iron Age oppida. Dorchester, located about two miles from the hillfort of Maiden Castle, can be viewed as its logical successor. Unfortunately, smaller towns and villages remain elusive.

There was also continuity in rural settlement. Many farmsteads dating to the pre-Roman period remained occupied and largely unchanged. There is evidence for Iron Age activity even at many villa sites, such as at Halstock, in Dorset. Here, the earliest phase of the villa was mid-2nd century, but the first occupation of the site dates to a Durotrigan farmstead of the mid-1st century BC. Farming was the most prominent activity in the Wessex countryside in the late Iron Age as well as early Roman period, and most of the primary crops produced remained the same. In general, Roman impact on the landscape was less the further you were from the road system and towns.

Evidence for continuity in the religious landscape is also apparent. The native British and Roman religious systems were compatible in a number of ways, including the veneration of sacred places in the landscape, the importance of ritual sacrifice, and corresponding festivals during the year. Many sacred sites from the pre-Roman period continued to be venerated after AD43. On Hayling Island, a late Iron Age temple in the parish of Northney was rebuilt in the early Roman period, to virtually the same exact plan and directly on top of the preceding one, only at a larger size. Religious continuity was fostered by the Roman tradition of religious tolerance.

Even at Bath, one of the most truly classical sites in Britain, evidence for continuity can be found, despite all the modifications which took place. The appearance of the sacred spring changed dramatically, but water cults are well attested amongst the Celts, and it is probable that the same Celtic goddess (Sulis) was worshipped here both before and during the Roman period. Unfortunately, the building of the Roman temple and bath complex removed most of the evidence for the pre-Roman use of the site.

In the industrial landscape there is again evidence for continuity, the main difference in the Roman period being the level of production. The Black Burnished pottery industry was well established prior to AD43, as was the salt production industry. The region remained primarily agricultural, despite the growth in industrial production. A coinage system was used by native tribes in the late Iron Age, as attested by the finds from the trading site of Hengistbury Head, and imports which were popular in the 1st century BC, such as wine and olive oil, remained in high demand.

In a strange sense, change itself can be seen as an example of continuity. Iron Age society had already been in a process of change before the Romans arrived. Abandonment of hillforts and the expansion of trade, for example, were already well under way before AD 43. So, as has been said in a different context, plus ça change, plus ça reste la même chose.

Debbie Day is a post-graduate student at St Cross College, Oxford


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© Council for British Archaeology, 1997