Catastrophe: An Investigation Into the Origins of the Modern World (5 page)

However, the most dramatic scenario of all is one in which a severe drought is followed by significantly increased rainfall. That, or something very much like it, is almost certainly what took place in East Africa during the worldwide climatic chaos of the 530s.

While weather was without doubt the motor that drove the spread of plague in East Africa, the key vector was the humble flea. Although the rodents were immune to plague, the fleas that lived on them were not. Fleas die of plague—but it’s actually the process of dying itself that helps them spread the disease.

As a flea becomes ill, and under specific climatic conditions, part of its gut becomes blocked by a mixture of multiplying plague bacteria and clotted blood.
¹²
The flea then begins to starve, and becomes so ravenous that it will jump onto virtually anything that moves, irrespective of whether it is its normal host species or not. Of course, the flea’s hunger will not be satisfied, because its gut is blocked. So it will move rapidly from host to host, biting each one—and consequently spreading plague—in an impossible mission to quell its hunger.
¹³
The disease itself thus produces the very mechanism for its own spread.

The species in East Africa that were probably the reservoirs for the disease were gerbils and multimammate mice. The sandy-colored gerbil normally has two litters (totaling ten offspring) per year. Gerbils are very territorial, and an individual will travel two to three miles per season in search of an area it can control as its own exclusive territory. Thus in optimal food conditions, when gerbil numbers increased, the need of each gerbil to find its own territory would have resulted in a wave of plague-carrying individuals spreading outward at substantial speed.

The multimammate mouse—a dark brown rodent about the size of a golden hamster—lives in colonies consisting of up to fifty individuals. Their gestation time is twenty-three days, and they have two litters per year. Normally they have only five offspring per litter, but when there is optimal food availability, the number can treble to fifteen. A pair can produce over a thousand descendants in a year. Today they are still a principal wild host of plague in Africa.

It is likely that the gerbils and multimammate mice then passed the disease to a ratlike creature in the genus
Arvicanthus.
The latter would not have been immune to plague, but in appropriate climatic conditions would have outbred even the multimammate mouse: In wet weather it can achieve densities of up to a hundred per acre, and it and its offspring can produce thousands of new individuals per year. Neither the multimammate mouse nor
Arvicanthus
is averse to invading human settlements, and would therefore have come into direct contact with nonimmune
Rattus rattus
—the black rat, a species that specializes in infesting human environments, including farms, storehouses, houses, villages, towns, markets, ports, and ships.

In good climatic conditions, one pair of black rats (also known as house rats and ship rats) can produce thousands of descendants each year, especially if their slower-breeding predators are rarer than normal (due to, say, a recent drought). The species is aggressive, highly adaptive, and able to eat virtually anything—insects, seeds, meat, bones, fruit, even each other!

Once the starving fleas had jumped in their billions from gerbil and multimammate to
Arvicanthus
and on to the black rat, it would have been only a matter of days, even hours, before the first humans started contracting the plague.
¹⁴

Transported by ships from port to port,
Rattus rattus
carried the plague bacterium from community to community. The archaeological evidence suggests that as the disease rolled northward up the Red Sea to Egypt, in its wake a whole way of life collapsed in East Africa and probably in southern Africa as well. The metropolis of Rhapta was inhabited by early Iron Age Bantu people, and the other ports of Opone, Essina, and Toniki were probably inhabited by late Neolithic Cushites, or possibly early Iron Age Bantu people.
¹⁵
At the time of the plague, as already noted, these ports seem to have virtually disappeared. Apart from Opone, their precise locations are not even known.

Inland, Bantu agriculture seems to have declined, and the Bantu appear to have rapidly and increasingly adopted from the Cushites both the latter’s cattle-based pastoral economy and their particular style of pottery. In the seventh century (i.e., after the plague had started), this cattle-based pastoral tradition began to spread south and supplant cereal growing all over southern Africa.

Two questions remain, however. How did the plague give an advantage to pastoralism (a livestock-based economy) over agriculture (a crop-based economy)? The answer lies in the number of rats and other plague-carrying rodents attracted to the two different economic systems. Food crops—whether in fields or in storage—attract rats. Food sources on four legs—in this case, cattle—do not. It was this difference that appears to have given pastoralism an advantage over agriculture at this critical time.

The second question is, what were ships carrying between East Africa and the Roman Empire? Ivory was one of the most valuable commodities needed by the empire. Demand for magnificent ivory chairs, exquisite ivory children’s toys for the rich, ivory writing tablets, religious relic boxes, and countless other ivory works of art had generated a trading system that no doubt stretched deep into Africa. Well before the sixth century, the elephants of Eritrea, on the Red Sea—used in antiquity as beasts of war—had all been hunted to extinction. So East Africa (modern Kenya and Tanzania) became virtually the only source for the vast quantities of ivory the Roman Empire desired.

Up until the plague and its destruction of the East African ports, the Roman Empire imported up to 50 tons of ivory every year from East Africa. This level of ivory trade necessitated the killing of up to five thousand elephants a year. In terms of cash, the merchandise was worth up to 220,000 gold
solidi
(equivalent to around $400 million today) to the Arab and Greek merchants who controlled the trade.
¹⁶

In East Africa, the trade sustained not only a series of ports but also a series of coastal chieftaincies, which must have exercised disproportionate amounts of local power through the trade goods and imported weaponry at their disposal. After the plague had substantially reduced the population and destroyed the ports, the ivory trade virtually ceased.

Between the year 400 and the eve of the plague (c. 540), of the estimated 400,000 major ivory artworks made, some 120 survive; from the period 540 to 700, only 6 survive. The surviving figures are so strikingly different that they show, without doubt, that after the mid–sixth century very little ivory was coming into the empire. The golden age of ivory artistry had been terminated by the plague.

A
century later, Mediterranean and European population levels had declined significantly, with Constantinople shrinking from a city of half a million to one of fewer than a hundred thousand inhabitants. Meanwhile, the mid-sixth-century climatic crisis and its consequences had been generating other mechanisms through which parts of Europe and Asia were to be transformed. The remote steppe of Mongolia was to become the unlikely source of change.

THE BARBARIAN
TIDE

D I S A S T E R  O N
T H E   S T E P P E S

I
n
A
.
D
. 557 or 558 a fierce Asiatic people called the Avars arrived on the eastern fringes of Europe from Mongolia. Twenty years later, they had conquered significant parts of the eastern half of the European continent and had humbled the Roman Empire by invading the Balkans, including Greece itself, either directly or by proxy through their vassals. They became a major element in the drawn-out process in which the empire gradually lost so much of its territory and its strength, and through which European and Middle Eastern history was fundamentally changed. But what caused the Avar migration has always been something of a mystery.

All that history records is that by
A
.
D
. 545, after 150 years of being the ruling ethnic group in Mongolia, Avar power was challenged by another Mongolian people—the early Turks. It is quite clear from the historical sources that the Avars had inexplicably become weaker in relation to their vassals, the Turks, and by 552 the Turks had turned the tables on their Avar overlords and taken over Mongolia.
¹
Many of those Avars who had not been slaughtered by the victorious Turks trekked west into exile, toward Europe.

To gain insight into the probable causes of this tribal revolution, let us look first at other similar changes on the Mongolian steppes, and at particular aspects of steppe ecology. Drought and famine on the steppes were what had finally precipitated the end of the Hun empire in the mid–second century
A
.
D
. at the hands of the Avars’ ancestors, who had inhabited the semimountainous terrain of eastern Mongolia and western Manchuria. And it is drought and famine that seem to have brought about the collapse of the now little-known Uighur empire around
A
.
D
. 840.
²
That famine weakened the once-powerful Uighurs through starvation and accompanying internecine strife, and made them sitting targets for subjugation by ferocious Kyrgyz tribesmen from the forests of the hillier adjacent regions.
³

Tree-ring, ice-core, historical, and archaeological evidence from around the world shows that there were major climatic problems in the 530s. More specifically, the records of the nearest literate civilization, north China, reveal that severe drought did kill many Chinese in
A
.
D
. 537 and 538. It’s highly improbable that the drought and famine stopped politely at the Great Wall of China; it must be assumed, with a considerable degree of confidence, that Mongolia too was hit by the disaster. Indeed, tree-ring evidence from Siberia—on the other side of Mongolia—reveals that in the years 535–545 the region suffered the worst climatic conditions in a 1,900-year period.
⁴

The catastrophe would have affected both the Avar and Turkic inhabitants of Mongolia, but the Turks would almost certainly have been less affected than their Avar masters. Although some Turkic tribes lived on the flat steppe, many inhabited the partly forested hills and mountains immediately to the north. The grass-covered steppe was (and still is) much more sensitive to drought than the forested uplands. Grass, with its short roots, cannot flourish in temporarily waterless conditions, whereas trees and even forest undergrowth, with much deeper roots, can tap into damper ground hidden well below the surface. Additionally, any clouds that were around would have tended to shed their rain when they arrived at the mountains. Even in drought conditions, mountainous areas normally receive more precipitation than adjacent plains.

The Turkic economy was also much more varied than that of the Avars. The Turks had, for instance, an involvement with hunting and gathering, with mining and metalworking, and almost certainly with goats, sheep, horses, and above all cattle.
⁵
The Avar economy, on the other hand, revolved predominantly around raiding, sheep, and horses. To the Avars, the horse was everything—a source of meat, milk, cheese, yogurt, and even alcohol (the sweet fermented mares’ milk called
koumis
). Moreover, the horse was the vital ingredient in Avar military power. It was what had made their ethnic group top dog in the Mongolian region for 150 years.