The exact nodes in this trans-Asian network varied over history, with consecutive empires routing the trade through their preferred cities, but this broad outline gives us a fair idea of the enormous, sprawling web of what we have come to call the ‘Silk Road’. And much of the great east–west communications network across the breadth of Asia passed through a particular climate band – desert.
The particular environment of the Silk Road was dictated by invisible movements of the atmosphere high above the heads of the travelling merchants. Around the equator, where sun-driven evaporation and rising air causes lots of rainfall, we find the dense tropical rainforests of our planet, stretching across the Amazon, the islands of the East Indies, and central and western Africa. (As we saw in Chapter 1, East Africa’s original rainforest was replaced by dry savannah due to the tectonic uplift of the Great Rift System.) But by the time this air has rolled over through high altitude and sunk back to the surface again, at around 30° north and south of the equator, it has become very dry: and here it creates the most arid regions on the planet’s surface. In the Southern Hemisphere, this dry band includes the Great Sandy Desert of Australia, the Kalahari in South Africa, and the Patagonian Desert in South America. In the mirror-image band stretching across the Northern Hemisphere lie the Mojave and Sonoran deserts in America, the Sahara, the Arabian Peninsula and the Thar Desert in north-west India.
The pattern is slightly more complicated in South East Asia, however. Here the desert band is disrupted by the monsoon system and its seasonal high rainfall. We’ll see in Chapter 8 how the Tibetan Plateau and Himalayas act to strengthen the monsoons over India, but these high mountains, and their offshoots like the Pamir, Kunlun and Tian Shan ranges, also act to block moisture-laden air from the Indian and Pacific Oceans from entering Central Asia. Many of the deserts, such as the Gobi and Taklamakan that the Silk Road had to negotiate, are created by this rain-shadow effect, and as a result the desert band in Asia extends much further from the equator than on other continents. Although some of these deserts are beset with shifting sand dunes – the Taklamakan is the second largest shifting-sand desert in the world after the Rub’ al-Khali that covers most of the southern Arabian Peninsula – many have a hard, pebble-strewn surface that is readily passable if you carry enough water supplies.
So not only did the crumpling tectonic uplift over the past 40–50 million years build the wide arc of the Himalayas but it also formed the deserts behind them. And it is both these deserts and the mountain ranges that defined the landscape the Silk Roads threaded across. Here one animal was uniquely suited to moving through this arid climate band and facilitate trade between east and west: the camel.
As we saw in Chapter 3, the camel evolved in North America and migrated across the Bering land bridge during an ice age several million years ago. While it died out in its birthplace, two varieties developed in the Old World: the two-humped bactrian camel in Asia (domesticated about 3000 BC)19 and the single-humped dromedary in the hotter deserts of Africa (domesticated around the second millennium BC).20 The camel’s ability to carry much greater weight for longer before needing rest, and its need for much less water, made it far superior to the horse or donkey for transport through these arid regions.
Contrary to popular belief, camels do not store water in their humps, which is in fact a store of body fat. Rather than distributing fat all over their bodies in an insulating layer, as many mammals do, camels use their humps as fat reservoirs, which provide energy while allowing the animal to remain cool. The camel is uniquely adapted to desert survival. After a week or so of trekking through an arid landscape, it can have lost almost a third of its body water with no ill effect – the animal can cope with such extreme dehydration without its blood becoming dangerously thick.21 The camel’s kidneys and intestines are able to produce highly concentrated urine and dung so dry it can be used to fuel a fire; it can also recapture moisture it would otherwise have breathed out,22 the water recondensing in its nasal passage like the drips from an air-conditioner unit. And the padded feet of the animal allow it to traverse such diverse terrain as desert sands, swamps or rock-strewn landscapes.23
Camels were essential for the trade in incense which began about 4,000 years ago. Although Arabia lies within the Earth’s desert band, in the south-west of the peninsula mountains capture enough rainfall from the summer monsoons to create a rare patch of vegetation. Here frankincense and myrrh can be extracted from small shrubby trees growing among these mountains. As they are best harvested in spring and autumn, their growing cycle is out of synch with the seasonal monsoon winds that facilitate sea transport up the Red Sea to Egypt or across to India, and so overland travel by camel was far more suitable. Caravans carrying incense skirted up the coast of the Red Sea through the Arabian Desert and then across the Sinai to Egypt and the Mediterranean, or they made their way east to Mesopotamia.24
In North Africa, camel caravans crossed the Sahara from about AD 300,25 bringing Sudanese gold to the Mediterranean. On their return the traders carried common salt mined from beneath the sands (which had been deposited by vanishing lakes as the Sahara desiccated) south to the trading town of Timbuktu, where it was loaded onto canoes and taken by river deeper into Africa. By the early thirteenth century the Empire of Mali had emerged, fed by the belt of fertile soil alongside the River Niger and its tributaries and by mining rich gold fields, and Timbuktu now became a royal city.26 The salt-for-gold trade persisted for centuries, and finding the mysterious source of the precious metal was one of the major motivations for Portuguese sailors exploring the West African coast in the early 1400s (to which we’ll return in Chapter 8).
Camels were also critical to the Silk Road crossing the arid latitude zone of Asia. Here too the animals were ideally suited for traversing diverse landscapes: sure-footed on their padded hooves over rock-strewn ground, and able to tolerate the climatic extremes between the deserts and high mountain passes.27 With a single pack camel able to carry a load of over 200 kilogrammes, and caravans easily numbering several thousand animals, their total cargo could rival that of a large merchant sailing ship.28
Although the arduous overland journey meant that in general it was high-value commodities that were moved along the Eurasian trade network, silk was not the only merchandise.fn4 Spices like pepper, cinnamon, ginger and nutmeg were carried west. India traded cotton and pearls, Persia exported carpets and leather, Europe sent silver and linen. Rome traded its high-quality glass, and topaz and coral from the Red Sea. Frankincense from the south Arabian Peninsula, as well as precious stones and dyes such as indigo, were also carried across Central Asia.30
But the huge importance of the Silk Road through history was not limited to trade goods. Together with the maritime trading routes along the southern coastlines of Eurasia, this extensive overland transport network also provided highways for the diffusion of ideas, philosophies and religions. Breakthroughs in mathematics, medicine, astronomy and map-making, as well as innovations and new technologies including the stirrup, paper-making, printing and gunpowder, all spread between peoples across Eurasia along these trade routes.31 The integrated overland and maritime networks were the internet of their time, allowing not just commerce over long distances but also the exchange of human knowledge.fn5
From the sixteenth century, however, the Silk Road began to lose its importance, as trade by land was outcompeted by the global oceanic network knitted together by European mariners in the age of exploration. The ancient Silk Road entrepôts, once some of the most vibrant places on Earth, lost their bustle and shine, and although some of the caravan stops, such as Samarkand and Herat, remain populous cities today, many other trading posts live on only in our cultural memory. It was the coastal ports that began to dominate global trade.
Nonetheless, for centuries the Silk Road was enormously influential for the movement of goods, people and ideas, as caravans threaded their way through mountain passes and across deserts. And it was the ecological zones and lands
cape of central Eurasia that created a fundamental distinction in the organisation of societies across the continent, leaving an indelible imprint on its history.
SEAS OF GRASS
We have seen how the bands of deserts running around the world are created by the dry, descending air of the circulation pattern in the Earth’s atmosphere (as well as the rain-shadow effect behind mountain ranges like the Himalayas). But the temperature gradient from the planet’s poles towards the equator also defines a series of layered climate zones, and the distinct ecosystems that are found within them.32 These horizontal stripes on our planet exist in both hemispheres but they are more pronounced in the Northern with its far greater land mass.
Here the northernmost zone, nearest the pole and stretching across northern Siberia, Canada and Alaska, is tundra. Very cold temperatures and a short growing season produce a bleak landscape in which little more survives than scattered dwarf shrubs, heath and hardy lichen clinging to rocks. It is populated only by reindeer herders or caribou hunters.33
South of the tundra lies the taiga, a stripe of dense conifer forests. This subarctic ecological zone covers most of Canada, Scandinavia, Finland and Russia, and gradually turns into the deciduous forests of Northern Europe and the United States at its southern limit. Whilst unsuited for agriculture or raising livestock, the taiga has been an important source of furs, including mink, sable, ermine and fox. In early modern history the demand for furs drove trappers across this taiga belt, and it turned Moscow into a major trade hub. In pursuit of furs, Russia expanded eastwards through the fifteenth and sixteenth centuries, across Siberia as far as the Pacific coast and the northern frontiers of the Chinese Qing Empire.34 In the seventeenth century, French and other European trappers similarly pushed through the Canadian forests.35 fn6
South of the tundra, our planet’s climate becomes temperate, before turning tropical closer to the equator. This pattern of ecological zones, arranged like stripes between pole and equator, has defined the lifestyles and economic possibilities of the people living within them throughout history. One ecological region in particular has had an enduring influence on the civilisations around the margins of the Eurasian interior.
Sandwiched between the northern, cold climatic band of the taiga and the chains of deserts to the south is a vast tract of grasslands. In Eurasia, this ecological zone is known as the steppes, and they sit in the same band of latitudes as the prairies of North America, with the Argentinian pampas and the South African veld appearing in the corresponding belt in the Southern Hemisphere.
Running through the centre of the Eurasian continental landmass, the steppes aren’t affected by the moist oceanic winds, and so receive little rainfall. This makes them too arid for most trees to survive, and the prevailing vegetation is drought-resistant grass. The grass in turn supports great numbers of ungulate mammals (many of which, as we saw in Chapter 3, originally evolved in this ecosystem). The steppes extend more than 6,000 kilometres in a continuous, broad belt from Manchuria to Eastern Europe. They are a vast sea of grass, larger than the entire continental US, but pinched in places into narrow corridors by mountain ranges; as a result they can be roughly divided into three main areas.
The Western or Pontic–Caspian Steppe runs from the Carpathian Mountains and the mouth of the Danube river, bordered by the Black Sea and the Caucasus to the south, all the way to where the Ural Mountains encroach within a few hundred kilometres of the Caspian and Aral seas. (The Great Hungarian Plain forms an island of grassland in the west, cut off from the main belt by the Carpathian Mountains.) The Central or Kazakh Steppe reaches from the Urals to the Tian Shan and Altai mountains, with the Dzungarian Gate in between, through which the northern route of the Silk Roads passed. The Eastern Steppe stretches from Dzungaria, through Mongolia, and along the northern margin of the Gobi Desert into Manchuria, until it reaches the forests that line the Pacific coast.fn7
The steppes are not an environment well suited to human habitation. Temperatures vary greatly between the seasons. In the dry heat of summer they can rise to 40 °C, and what rain there is falls in heavy thunderstorms. In winter, under the cloudless skies, the steppes become bitterly cold with temperatures dropping to –20 °C or less, the ground gets smothered in deep snow, and howling winds scour the flat landscape. But most significantly, with little vegetation beyond tough grass that our gut cannot digest, the steppes have not much to offer hunter-gatherers and present a formidable barrier to those travelling on foot. To survive in the steppes, you need mobility as well as a way of generating food.
While the camel was ideally suited to Earth’s desert band, the grassy steppes stretching across central Eurasia provide a perfect habitat for the horse. The natural range of horses around the world shrank dramatically between 10,000 and 14,000 years ago with the closing of the last ice age. The horse fell extinct in North America, and as the world warmed the species also disappeared from the Middle East. With the retreat of the ice sheets wide areas of dry grasslands across northern Eurasia were replaced by dense forests, and in Europe the horse survived only in a few isolated pockets of natural pasture. But in the steppes of Central Asia, horses and their equid relatives became the most common grazing animals, and here they were hunted by the Neolithic tribes. Archaeological evidence indicates that more than 40 per cent of the meat in their diet came from equids.
The ecological band of the steppes reaching across the spine of Eurasia.
In fact, horses were at first domesticated not for transportation, but for food. Cattle will not graze grass if they cannot see it through the snow, and the tender nose of sheep allows them to feed only through soft snow. Both are therefore liable to simply stand and starve to death in a winter pasture with forage just beneath their feet. The horse, however, is well-adapted to the cold grasslands and can break even through icy, compacted snow with its hooves to uncover the winter grass beneath; it is also instinctively able to crack through frozen-over water to find drink. Indeed, the trigger for humans to begin domesticating horses may well have been climate change that brought colder winters to Eurasia.37 This was achieved possibly as early as 4800 BC in the steppes north of the Black and Caspian seas.38
Humans learned how to control and ride the animals, and this proved utterly transformative. As we saw in Chapter 3, it was the domestication of grazing mammal species like sheep and cattle that bestowed on humans the ability to convert grass into nutritious meat and milk. Yet settled farmers have limited pasture available for their livestock and this can get exhausted quickly by grazing animals. Herders on horseback with vast grasslands at their disposal could range far further and control much larger herds. In addition, the introduction of solid-wheeled wagons, pulled by oxen, from Mesopotamia around 3300 BC gave the steppe peoples the opportunity to take with them all they needed39 – food and water supplies, tents for shelter – and roam freely for long periods with their herds across the vast grasslands.40 This combo package of herbivorous ungulate livestock, fast-moving horseback riding and oxen-pulled wagons serving as mobile homes opened up the steppes for widespread human habitation.fn8
Irrigated agriculture for cultivating grain is possible only in the more fertile areas along the few rivers that cross the steppes. So on the whole people survived here as pastoral nomads: by raising livestock and constantly moving with their herds between different grazing grounds, following the seasons.43 And the landscape of the steppes presents few obstructions to overland movements. This core region of Asia is tectonically ancient terrain, uncrumpled by recent plate collisions and rubbed flat by erosion. While the southern margin of Eurasia is characterised by great mountain ranges, the band of the steppes running through the middle of the continent is largely free of such barriers. The exception are the Ural Mountains, one of the rare chains in Asia that run in a north-south direction,44 separating the Western and Kazakh steppes and constricting travel to a narrow passage between their bottom tip and the Caspian Sea.fn9 But apart from the Urals, there are few natural barrie
rs like marshes or forests. Horsemen and carts can rove easily across the steppes, turning them into a vast natural highway that sprawls right across the continent and which came to shape the history of Eurasia as a whole.
These nomads entered into an uneasy relationship with the settled agrarian societies around the margins of the continent, ranging from peaceful yet tense coexistence to armed conflict. They traded their herds and their animals’ products – cattle, wool from their sheep, and especially the horses they bred in large numbers on the grasslands. They also hired themselves out as mercenaries in the armies of the Eurasian civilisations, often helping to guard their frontiers against incursions from other nomad tribes. They demanded protection money from merchant caravans passing through their lands, or they would ambush them. But they exerted their greatest influence on the course of Eurasian history when they emerged from the depths of the steppes in large numbers to invade the territories of the civilisations settled around the rim of the continent.
Horse-riding nomads were a formidable foe for these agricultural and maritime societies.46 At times they demanded tributes and could be paid off; at others they raided farms and villages for plunder, and after pillaging what they could carry, they would simply melt back into the vast expanse of the grasslands. Without substantial numbers of their own mounted cavalry, the armies of the agrarian societies could not pursue them into the sea of grass, the arid plains offering no food to support campaigns of foot soldiers. And repeatedly throughout history, loosely aligned in large confederations, nomadic tribes erupted out of the steppes to invade and conquer the settled civilisations, at times forging huge empires that stretched across Asia.47
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