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More than 4,000 years ago, a wall seems to have gone up across what is now northern Iraq.
It may have been over 200 kilometers long – more than the distance between New York and Philadelphia; just a little less than the distance from Paris to Brussels.
It appears to have stretched between the Tigris and Euphrates rivers. And evidence survives for its construction because its laborers worked for the third dynasty of Ur.
Ur was one of the world’s first great cities.
The dynasty was an administrative state like few others in the ancient world. From its nerve center in Ur, it counted, moved, then recounted livestock, grain, textiles, and workers across a vast stretch of Mesopotamia – today’s southern and central Iraq.
To keep track of it all, the bureaucrats in Ur, and imperial centers like Drehem and Nippur, chiseled into clay tablets – lots of them. More than 100,000 survive. Together, they offer remarkably detailed glimpses of how a truly ancient state managed its people and resources.
Like so much evidence for humanity’s deep past, the tablets of Ur tell us that we’re not as special as we might think. That the ways we organize ourselves, which we often view as so quintessentially modern, actually have ancient roots.
Enter the wall.
A few dozen tablets mention labor teams assigned to the wall, or rations issued for wall work, or officials who travelled to the wall, and along the wall. A handful of tablets, proclaiming the dynasty’s great achievements, also mention the wall’s construction.
Now, we might be skeptical that a wall some 200 kilometers long could be built, so long ago. We might doubt the evidence in the dynasty’s tablets. Except, archaeologists have uncovered long, linear earthworks in Iraq that may suggest that the wall really did exist.
But why? Why build such a monstrous structure, over 4,000 years ago?
Well, the wall went up after the collapse of one of the world’s first great states – the Akkadian Empire. And the tablets suggest that it kept out the Martu, a catchall phrase for groups of mobile pastoralists who, supposedly, took advantage of the abandonment of cultivated land.
The Martu peoples seem to have moved in when the Akkadian empire disintegrated. If so, the wall appears to have controlled their movement, channeling them away from the irrigated land on which the dynasty in Ur depended.
So, why did the Akkadian Empire fall apart?
No doubt there are many reasons. But compelling evidence now indicates that it collapsed amid one of the worst droughts of the Holocene, a multi-centennial megadrought that few states could have survived.
If so, then the Wall of the Martu, as the Ur dynasty called it, may have blocked the movement of climate change migrants.
Clay tablets and linear embankments. Together, they tell a frightening story. An echo from the ancient past of a possible future – of walls, refugees, and climate breakdown.
Welcome to the 16th episode of The Climate Chronicles, the fifth and final episode of our third season, “Into the Holocene.”
In this episode, we’ll explore what may be the most extreme and widespread drought of the Holocene: the so-called “4.2 ka BP Event.”
As we’ll see, many aspects of the event remain mysterious, even controversial. But it seems that, about 4,200 years ago, an extraordinary wave of drying swept across parts of the tropics, from North America through Africa, into Mesopotamia, and across South and East Asia. In some regions, drought may have stretched on for centuries.
Why did it happen? How did people respond in one of the world’s first agricultural civilizations? What vulnerabilities, and possibilities for adaptation, did a big agricultural civilization possess? And what does it mean for a society to collapse?
In this episode, we’ll explore all of these questions, and more.
By about 5,000 years ago, populations across Africa, Europe, and Asia had discovered bronze.
Creating bronze was a formidable challenge. Turning it into something useful was even harder. First, you had to mine copper, which is abundant, but then you also had to mine tin or other rare substances to mix with the copper – a process called alloying.
Once you had enough copper, you had to heat it up, melting it or, actually, smelting it to separate metal from ore. You had to do the same to tin, or whatever else you chose to mix with the copper. And you needed a way to create a lot of heat, because although tin’s melting point is low – not even 300 °C – copper’s is almost 1,100 °C.
About 5,000 years ago, kilns could just barely manage that.
Now, when you had the liquid metals and mixed them together, you had to pour them into a mold. There, the bronze alloy would cool into needles or axes or blades or ornaments –whatever you wanted to make.
And the mold had to be well crafted. I know from experience. My father, Bas, was an artist. Towards the end of his life, he won commissions to craft a series of bronze statues.
I was a young teenager when I helped Bas make some of those statues in his workshop. I watched as my dad carved into clay, shaping sculptures, around which he built plaster molds. Occasionally, I held onto those molds as my dad filled them with wax. Eventually, we’d split the plaster molds, and then Bas worked with the wax statues inside, perfecting them.
Now we created new molds around the wax. Finally, Bas took the molds to a foundry, where they were filled with molten bronze. The liquid bronze melted away the wax, then cooled into rock-hard statues. Even then, Bas usually didn’t think they were ready; my dad used a circular saw to cut through the bronze and finish his statues.
It was grueling, messy work. And the red-hot bronze – not to mention the saw, grinding through metal – made it dangerous. I can only imagine what it was like, more than 5,000 years ago, when Neolithic smiths tried out bronzeworking for the first time.
But it was worth it. You might assume that bronze was valuable because it could be used to create things that were harder, or more durable, or sharper than anything people had worked with before. Or you might assume that the advantage of bronze lay in its repairability, because bronze artifacts could be melted down and remade if they were damaged.
That’s all true, but the real advantage of bronze was that it unlocked something we might take for granted today – the ability to create an object with fine detail, in any imaginable shape. Shapes and in turn artifacts could be optimized – or in other words, tailored for a specific function – and they could be standardized, so everyone in a population had the perfect tool with which to cut down a tree, for example, or collect the harvest, or build a house, or sew a garment.
The use of bronze was so revolutionary that its origins have inspired yet another way to organize human history. Remember, one way is to think about climatic periods – the Pleistocene with its glacials and interglacials, and then the relatively stable Holocene. A second way is to distinguish between the Paleolithic, Mesolithic, and Neolithic.
And a third way is to focus on the materials that people used for their tools, because these materials enable and are enabled by different ways of organizing human life. We can divide the Stone Age – the overwhelming majority of human history – from the Bronze Age, which began over 5,000 years ago.
The Bronze Age followed different chronologies in different populations, and in some regions – Australia, for example – it never happened. In one region, the Middle East, some archaeologists distinguish between a millennium-long early Bronze Age, and a middle and late Bronze Age lasting about five centuries. In any case, after the Bronze Age came the Iron Age, which we’ll discuss next season.
This third way of understanding human history is just as messy and problematic as the others, but it captures something important. Bronzeworking was indeed transformative. That’s partly because it didn’t just confer new powers on populations. It also requirednew connections betweenthem.
After all, copper was easy to get in most places, but the metals or minerals that had to be mixed with copper to create bronze – usually tin – were scarce, which meant they often came from distant sources. Bronzeworking therefore depended on long distance trade. It encouraged populations to form new political and economic connections.
And bronzeworking created new possibilities for social stratification, for inequality. Bronze could be turned into jewels, ornaments, statues, and ceremonial objects – giant or intricately detailed bowls, for example – and these artifacts reinforced inequalities that seem to have emerged, or at least, intensified, in the Neolithic.
As we’ve already seen, agriculture had created surpluses, extra food that needed to be stored. Actually, this is one of those fascinating moments in human history where something that seems objectively good – having more food – turned out to have all sorts of unintended consequences. Because excess food had to be stored, and stored food was valuable, so it had to be defended.
More and more reliable food allowed for larger populations, and it freed some people from working on the land. Many of these people were encouraged – or compelled – to build things, while others moved and sold goods, or people. Artisans forged equipment or weapons that soldiers used to protect stored food and the communities that depended on it.
Big surpluses also cried out for people who could keep track of stored grains, or manage access to those grains, or redistribute them. And the need for surpluses created demand for those who could appease the gods to ensure good harvests.
Enter the priest. In growing agricultural communities, priests were more than shamans. They oversaw the rites that supposedly ensured the success of the harvest, and they managed land, or food storage, or both, while keeping records, calendars, and preserving knowledge of, for example, medicine.
Priests also legitimized the person who could organize all the new labor: the chief or, in really big populations, the king. And so did the new bronze commodities. Artifacts displayed the power of the king. They signaled his superiority. Because they were durable and had value, they could be hoarded or gifted, so they directly fortified the king’s power.
What’s more, the trade networks that bronzeworking demanded could be controlled. And all this meant that the Bronze Age didn’t just mean that people had new, better tools. It also meant that populations now faced powerful pressures to organize themselves in more and more unequal ways, and then to fight for control of resources.
The Bronze Age would be an age of empire.
Stockpiled grains, bronze equipment, precious artifacts, even fields and herds: they were all lootable resources. That’s a term coined by my colleague, Luke Kemp, and it captures something important: the Bronze Age gave expanding agricultural populations a critical mass of things that could be given – and taken.
With some important exceptions, populations that relied on agriculture also couldn’t move like their hunting and gathering ancestors. Nor could most migrate like herders, or pastoralists – people who lived mainly off their animals.
Admittedly, some populations practiced versions of both pastoralism and agriculture. Many, however, specialized in one or the other, especially after about 7,000 years ago. Pastoralists thrived on the world’s grasslands and scrublands, where crops couldn’t be grown. We’ll come back to them later in The Climate Chronicles.
But for now, our focus is on the agriculturalists of the late Neolithic, about 6,000 years ago. Agricultural communities were rooted in place, just like the plants on which they depended.
That was partly why they had more children than hunters and gatherers. Infants were difficult to carry on treks from environment to another, but of course that wasn’t a problem for sedentary communities.
Farmers could also feed their children porridge, gruel, and animal milk. Women didn’t have to breastfeed for as long, so they became fertile sooner after childbirth. And compared to foraging, farming yielded more and more predictable food in the same amount of land, meaning more people could be fed. It also required more labor, including child labor, so families benefitted from having kids as they hadn’t before.
All of this this means that in the middle Holocene, more and more people were, in effect, caged, as Kemp puts it. In one captive population after another, a handful of people gained power, and with it the ability to monopolize weapons that now targeted other people, rather than animals.
To Kemp, those three conditions – lootable resources, caged populations, and weapons that could be monopolized – nourished a monster that was genuinely new in human history. It’s a monster that may dominate our world today, and it’s what Kemp calls Goliath.
Goliath, to Kemp, is a collection of hierarchies in which a small group of people dominate a big group by controlling supplies of energy and labor. The small group finds ways to legitimize its power, but its power is ultimately sustained and perpetuated through violence, or the threat of violence. It’s why that monopoly over weapons is so important.
Goliath is a system of domination that, to Kemp, looks similar from one from society to another, across history. And it’s a system you may recognize today. After all, even in our world’s most egalitarian countries, power ultimately resides with a handful of people, and ultimately depends on coercive institutions: the police, military, and intelligence services, all of which claim the right to use violence.
Kemp argues that Goliath’s birth represents a kind of metamorphosis in human populations, a transition from living like other primates, which we did for about 300,000 years, to living like social insects – ants, bees, or termites.
I think this is an interesting idea. But before we explore its full implications, we should point out some of its limitations.
First, as a historian, I’m contractually obligated to point out that when someone suggests that the same thing pops up again and again throughout history, I’m always a little skeptical.
You see, historians tend to find differences between populations, between times and places, rather than similarities. We’re instinctively wary of reductionism, the idea that we can understand things better by breaking them down into their constituent parts.
There’s good reason for that. In our research and teaching, we historians usually focus on a particular time and place. There’s no better way to appreciate the unique qualities of different populations and cultures, or the difficulty of comparing them across time and space. The idea that most agricultural societies created exactly the same kind of domination system, made of the same basic parts, runs into a historian’s natural tendency to focus on diversity.
Second, the concept of Goliath has a hint of presentism about it. That’s when we see in the past what we perceive around us in the present, often without meaning to. The trouble with that kind of thinking is that it can lead us to distort the past, to exaggerate its similarity to our time, or rather to our interpretation of our time.
After all, if you think you live in a political and economic system that oppresses you – and there’s good reason to believe that – then you might expect to see similar systems in the past. And even the most careful scholars tend to find what they think they’ll see.
All of this means that Goliath is not just a neutral idea, an academic’s interpretation of a phenomenon in the distant past. No, the concept is rooted in present-day politics.
You may think you live in a democracy, with control over your government and agency in your economy. But to Kemp, at least some of that is window dressing for a system of domination: Goliath. It’s an idea that invites us to challenge the system, or at least to moderate its worst excesses, so it’s an idea that has an explicitly leftwing, maybe even anarchist orientation.
In my view, reasonable people can have different interpretations of both the past and the present.
Now, even if you subscribe to the idea that Goliath really did exist in one society after another – and let’s assume you do – then, third, we have to distinguish Goliath from other concepts that describe changes in human populations during the late Neolithic. And that requires us to add some complexity to the neat and tidy origin story I just provided – the story where lootable resources, caged populations, and weapons that can be monopolized all add up to create a monster.
The fact is, Kemp’s Goliath didn’t automatically form wherever populations practiced agriculture. It didn’t even emerge anywhere that human populations, once relatively small and isolated, coalesced into a complex society, like a Bronze Age empire.
And here’s another concept we should definitely pause to unpack. Because, if you listened to the first two seasons of The Climate Chronicles, that term – complex society – may sound a little strange. We’ve seen how Paleolithic, Mesolithic, and early Neolithic communities were diverse, flexible, innovative, and more or less connected. That certainly sounds plenty complex.
As my colleague John McNeill puts it, “people who lived in complex societies were no better or worse, no smarter or dumber than those who didn’t,” and that’s why, “every society, even a small hunting and foraging band, is complicated.”
But McNeill points out that, at least according to social scientists, “not every society is complex.” It’s because the term, complex society,refers to something very specific: a big group of people, with, as McNeill writes, “an elaborate division of labor, a pronounced social hierarchy, hundreds of different social roles that people can fill, and institutions to regulate exchanges among individuals and among groups.”
To Kemp, a complex society often gave rise to a Goliath, but not always.
No – Kemp thinks that Goliath grew out of the early state, which in turn took root in most complex societies. You probably already know a good definition for the state. It’s actually similar to the definition of Goliath, because a state is a territory controlled by a small group of people – a political community – that forms a government and claims a monopoly over violence, meaning only it can legitimately use violence.
A state also demands things from a population. Those things invariably include loyalty and obedience. They could, at times, also include commodities, such as grains, or labor, and eventually they almost always included money – what we call taxes.
And a state usually had a set of ideas to justify its existence, or in other words an ideology typically rooted in a religion with deities, or a deity, who judged bad behavior. Now, faith had many functions. I do believe it connected people to something real, something bigger than themselves. But there’s little doubt that the prospect of punishment for the wicked, after death, also persuaded ordinary people to accept the state, with all the inequalities it created or enshrined. And maybe it tempered some of those inequalities by moderating the behavior of elites.
Now, states emerged with cities, and by this I don’t just mean a big village. A city is distinguished by its size, yes, but also by the divisions of labor and social hierarchies that exist within it. Its people are tightly packed together, in dense housing, but they have big open spaces and imposing public buildings. They organize flows of trade, both within their boundaries and between other populations, and they have ways to connect buyers and sellers – through markets, for example.
Complex societies, states, and cities all emerged at the dawn of the Bronze Age, about 5,000 years ago, and I think now it’s easy to understand why. As we’ve seen, long distance trade, division of labor, division of power, even the ideologies that justified states – all encouraged and were encouraged by bronzeworking.
And to Kemp, they gave birth to Goliath.
Now, one could argue that Goliath is just a rebranding of the state. That would still be valuable, I think, because historians – swayed by what Kemp calls the 1% view of history – have tended to imagine the Bronze Age as a time of growth and progress.
And to some extent, it was exactly that. The emergence of complex civilizations, the growth of the city, the strengthening of long-distance trade: it was all revolutionary, and it nourished the development of fundamental ideas and technologies, not just bronzeworking but the wheel, the written law code, public administration, urban planning, the list goes on, and on.
Maybe the most important consequence of these achievements was the creation of more durableand detailedknowledge. Information could be preserved in writing, then stored and added to by specialists, and then shared across long distances so that if knowledge was lost in one place, it survived in another.
The Goliath concept draws our attention away from these very real and species-altering achievements and towards the systems of dominance and violence that emerged with them, required them, and helped make them possible. And the concept honors a disturbing feature of many new Bronze Age societies. Their subjects were, on average, less healthy and – probably – less happy than their ancestors.
We know because of the skeletons they left behind. Those skeletons are short – a good proxy for poor nutrition and disease – and they show signs of wear that must have come from grueling, repetitive labor.
We’ve seen that the isotopes in teeth and skeletons can reveal diets, and the isotopes in Bronze Age skeletons suggest that many people ate just a few staple crops, meaning they didn’t consume enough nutrients. Cavities and signs of tooth loss and dental abscesses all tell us the same thing. The ancient DNA of pathogens, preserved in skeletons, suggests chronic infections.
The key point is that, for the first time in human history, people didn’t have similar lives. They didn’t experience the same hard and good times. Because the skeletons of elites within the same Bronze Age populations don’t show declines in height, or nutrition.
What’s more, relations changed between the sexes. When compared to other animals – even other primates – humans have relatively low sexual dimorphism. There’s only about a 15% difference in average body size between females and males – compare that to 50% for gorillas and orangutans.
Low sexual dimorphism made evolutionary sense for a big-brained species. It discouraged intense competition for mates, and seems to have encouraged males to take an active role in rearing offspring that, when compared to other baby animals, took a very long time to mature.
All evidence indicates that relations between women and men were relatively egalitarian in most Paleolithic and Mesolithic communities. And although we may assume that a strict division of labor characterized most of these communities – men hunted, women gathered – new discoveries show that this often wasn’t the case.
Things began to change in the Neolithic. Lootable resources created new opportunities not just for hoarding wealth, but also for passing it on to the next generation. Because maternity is usually obvious, but paternity is not, these changes created incentives for men to regulate women’s sexuality. By controlling who had sex with whom, men could ensure that wealth passed to their biological offspring.
Over time, agricultural populations gradually organized themselves into households dominated by men, and lifelong bonds between men and women – in other words, marriage – evolved into economic institutions. Eventually, unequal relationships between men and women were formalized in the laws of Bronze Age states.
In short, the human experience had become bifurcated between the haves and the have-nots, the oppressors and the oppressed. Systems of domination were nested within each other, on scales ranging from the family all the way up to the society.
The Goliath idea helps us appreciate how life changed, and in many respects deteriorated, for the 99%. It lets us see that new divisions, new forms of control and violence, were among the most important legacies of the Bronze Age.
In my view, it’s an important corrective to that 1% view of history.
So, yes: the Bronze Age was a time in which complex societies emerged, independently, in different parts of the world. In some places, these complex societies gave rise to cities and states, which encouraged the emergence of dominance hierarchies – Goliaths – that, for growing multitudes, transformed the experience of being alive.
In episode 12, we saw that agriculture was invented and perfected by ants. And it seems that, when some of us adopted the ant way of life, we also took on their way of organizing themselves.
In the Bronze Age, more and more human collectives became like ant colonies: populous and centralized. These new communities would have new vulnerabilities to climate change – and new ways of resisting and adapting.
Goliath was born in two places: the Nile River Delta, and Mesopotamia’s southern alluvial plain, between the Tigris and Euphrates rivers.
In this episode, we’ll focus on Mesopotamia. In later episodes, we’ll come back to Egypt, then move on to other regions where complex societies and, in most cases, Goliaths independently emerged.
In all these places, mountains and rivers were central to the story. In Mesopotamia, for example, moist air rising over the Taurus and Zagros Mountains cooled, and in cooling released its water as snow. Every spring, the mountain snow melted into the Tigris and Euphrates rivers, which flooded, and by flooding gifted water and silt to the Mesopotamian lowlands.
In theory, these gifts were ideal for agriculture. In practice, they came too early in the year for grains grown in the hot, dry Mesopotamian climate of the middle Holocene. There, and then, grain seeds had to be sown in the fall and harvested in the spring. The challenge was to figure out how to bring the spring water to soils just before seeds were planted in the fall.
Irrigation – the use of artificial channels to siphon water from lakes or rivers to fields where crops are grown – solved that problem. Neolithic populations in the Levant and northern Mesopotamia seem to have invented irrigation thousands of years before the Bronze Age. But it was only about 5,500 years ago that irrigation spread widely and reached scales that allowed it to sustain truly big populations.
Mesopotamia was a perfect place for irrigation not just because of its climate and river floods, but also because the Euphrates is generally at a higher elevation than the Tigris. Farmers could dig channels that directed water from the Euphrates to farmland, and then drained that water into the Tigris.
Irrigation changed the possibilities for expansion and development in Neolithic communities. It raised the quantity of grain that could be grown per acre of territory by up to ten times, and it created habitats for tasty morsels like fish and snails that could, of course, also be eaten. It created a new kind of ecosystem, a hotbed of food for people that could sustain populations of previously unimaginable size and density.
But irrigation was also precarious. The canals, dams, dikes, and ditches on which it depended required constant maintenance, and were obvious targets for armies or bandits. Irrigation also created ideal environments for parasites that plagued newly dense populations. Worse, it eroded soil, drained it of nutrients, and filled it with salt.
Unless farmers carefully managed erosion (by building terraces, for example), replenished soil nutrients (the best option was to use manure) and drained soils to prevent the buildup of salt, irrigated ecosystems survived on borrowed time.
And cities hastened their demise. Whereas nutrients had been returned to irrigated ecosystems in smaller villages – through manure, for example – cities extracted nutrients and then, often, drained those nutrients into rivers, which worked like sewers to dump them into the sea. So, cities took nutrients from soils, but didn’t give them back.
Ultimately, irrigation created both brand new vulnerabilities and new sources of resilience in the face of climate change.
It left populations of unprecedented size precariously dependent on ecosystems that, in turn, relied on regular precipitation. And these populations couldn’t simply move to greener pastures when the snows and rains didn’t come.
Although there was more food to go round, we’ve already seen that most people in agricultural communities were also malnourished compared to hunters and foragers. Not only were their bodies generally less capable of surviving multiple missed meals, but many also ate barely enough to get by, even in good times. Small shortfalls in food availability were therefore more devastating for many people in agricultural societies than they had been for hunters and gatherers. And the inequality in complex societies meant that when dearth hit ordinary people, they tended to blame the elite, which could mean violence, even civil war.
At the same time, irrigation could reduce the vulnerability of populations to local changes in temperature or precipitation, because it was meltwater from the distant mountains that had the biggest impact on river floods. Better yet, the complex societies and states that irrigation nourished and sustained could use the infrastructure that came with irrigation to buffer their populations against short-term anomalies in climate. Water reservoirs, for example, typically didn’t drain in one season of low rainfall, while granaries could stockpile harvest surpluses that could usually last for several years of poor harvests.
Best of all, big populations that depended on irrigation had developed long-distance trade networks in the Bronze Age that – at least in theory – allowed good harvests in one region to make up for bad harvests in another.
So, we can think of this way: the big, dense populations in complex societies that depended on irrigation and were governed by Goliaths were usually less vulnerable than other populations to climate shocks on small scales in time and space, but often more vulnerable to long-term, regional or even global climate trends.
Now, the world’s first cities emerged in a relatively stable climate. About 3500 BCE – that’s 5,500 years ago – the mud-brick village of Uruk started to become different from other such settlements across southern Mesopotamia. The town was well-placed, at the nexus of trade routes that increasingly crisscrossed the region.
Within a couple hundred years, Uruk had become the world’s first city-state, meaning a city surrounded by farmland it controls. Its people imported limestone, and heaped it into hulking ziggurats: temples, then temple-palaces. Eventually, up to 80,000 people lived in the shadow of those ziggurats.
Other city-states – Ur, for example, and Lagash – popped up nearby, and proximity led to competition that, for the first time, spurred largescale conflict – or in other words, war.
It was also the first time in human history that a peculiar condition had emerged – a condition in which a cluster of small but fiercely independent little states duke it out in the same narrow territory. I believe that, from ancient Greece to Renaissance Italy, competition in these circumstances has been a powerful engine for innovation.
And indeed, in Sumer – the collective name for Uruk and its sister city states – the inventions came at a speed that was, at that point, unprecedented in human history. From cuneiform writing to beer – women at Uruk could brew about 70 varieties – innovations swept across Mesopotamia.
Legends preserve the tale that, around 2340 BCE, a priestess in a small city-state named Kish gave birth to a boy, Sargon. Supposedly, she loaded little Sargon into a reed basket and set him adrift on a river, where he was found by a poor family and made to work in an orchard.
It’s a prelude to the story of Moses – which came later – but after he grew up, this boy made a rather different career choice. Instead of leading his people out of slavery, he consolidated power in Kish, created history’s first professional army (equipped with cutting edge bronze weapons), and used that army to conquer, and enslave, hundreds of thousands across Sumer.
Clay tablets from across Mesopotamia inform us that Sargon established a new capital, Akkad. Its remains haven’t been found yet, but they may lurk beneath today’s Baghdad. During Sargon’s 56-year reign, Akkad became the nerve center of something new: a state that expanded, through violence, to absorb or control other states, territories, and peoples.
There’s a word for this: empire. And empire supercharged Goliath. In a couple centuries, Goliaths had grown as small villages with chiefs mushroomed into cities with kings. Now, in just a couple decades, individual Goliaths had merged into a vast system that dominated up to one million square kilometers, and perhaps two million people.
To put that in perspective: the entire human population at the end of the Pleistocene might have equaled that of the Akkadian Empire.
But shortly after Sargon died, in 2279 BCE, his empire began to crumble. In about a century, it was gone. You see, the emergence of history’s first empire couldn’t have come at a worse time – at least for its leaders. The reason? Quite possibly the worst drought of the Holocene.
Meghalaya is the name of a state in Northeastern India. It’s a name that translates in Sanskrit as “abode of clouds,” and rightfully so: it’s one of the wettest places on Earth.
Near Cherrapunji, a town strung across an emerald forest more than 4,000 feet above sea level, slightly acidic rainwater has slowly wormed its way into limestone. Over time it hollowed out Mawmluh Cave, a system of caverns some seven kilometers long.
Meghalaya’s heavy rains feed a steady drip of water into the cave. In the dark, the dripping drops minerals that feed some of the most impressive stalagmites and stalactites in India. And because the dripping is constant, those speleothems record changes in the region’s water with an unusually high precision, or resolution.
If you’ve listened to our first 15 episodes, you may suspect that the key change is the ratio of light to heavy oxygen isotopes in that water. You’d be right. And this change reflects the strength of the Indian Monsoon.
The reason is that water molecules with heavy oxygen are slightly heavier, so they condense into raindrops more easily than molecules with light oxygen. When moist air rises and cools, raindrops at first remove heavy oxygen from clouds. And if that air keeps raining – as in a strong monsoon – then this happens again and again, so the remaining moisture is depleted of heavy oxygen.
By the time the water falls at Mawmluh Cave and drops down to form speleothems, it has a high ratio of light to heavy oxygen isotopes. But if the monsoon is weak, more heavy isotopes end up in the speleothems, and the ratio is lower.
Now, in 2014, a team of scientists studied a stalagmite from Mawmluh Cave and found something remarkable: a sustained stretch of heavy oxygen isotopes in minerals dated to 4,200 years ago. It seemed like clear evidence of a collapse in the strength of the monsoon – a collapse that lasted as long as two centuries.
It appeared to be such an extreme event that geologists decided that a new unit of time had begun.
Now, in our second episode, we saw that an epoch is one of the shorter units of geological time. That’s true, of course; we’ve only been in the Holocene for about 11,700 years. But epochs can also be divided into even shorter ages.
In the Holocene, the Greenlandian Age started 11,700 years ago, then ended 8,200 years ago. The subsequent Northgrippian Age lasted until around 4,200 years ago. Both of these ages are named after ice cores in Greenland, which record abrupt warming about 11,700 years ago, then sudden cooling – driven by meltwater spilling into the Atlantic – around 8,200 years ago.
The Meghalayan Age started 4,200 years ago, with the collapse in the strength of the Indian Monsoon that the Mawmluh Cave stalagmite appears to record. Because it’s not just that the monsoon suddenly lost a lot of its power. No – it seems that a wave of drying swept across much of the world.
Speleothems from across East and South Asia suggest long stretches in which monsoon rains were much weaker than they had been. Speleothems, together with seabed and lakebed sediments, also indicate that in the Middle East, precipitation may have declined by a third, perhaps even half, beginning about 4,200 years ago. We’ve already seen that the Sahara dried out at around this time. Lakebed sediments even suggest that decades-long droughts swept across parts of North America.
At the same time, ice cores and seabed sediments indicate cooling in the far north and south, complete with advancing glaciers, while speleothems and even fossilized tree rings suggest wetter conditions outside the tropics – in northern and central Europe, for instance, or sub-Saharan Africa, and parts of China. Actually, some speleothems don’t show any drying at all – a reminder of just how difficult it is to reconstruct climate change even in the middle Holocene, let alone in the really deep past.
Overall, it seems that, for a couple centuries, waves of extreme drought stretched across the equatorial regions, from one end of the world to the other, while moisture increased in the mid-latitudes, and temperatures dropped at the poles.
But it’s increasingly clear that this “4.2 ka Event” was, perhaps above all, complicated. Changes in precipitation and temperature definitely didn’t unfold in the same way everywhere, or from one decade to another. In some regions, the onset of drought seems to have been in abrupt, while in others it was the conclusion of a long-term trend. That’s partly why some dispute that a Meghalayan Age actually began 4,200 years ago.
What’s more, the reasons for the period’s shifts in temperature and precipitation are still difficult to piece together. Multiple possibilities have been proposed. It may be, for example, that the Sun underwent a prolonged period of relatively low activity, and that a slight drop in the solar radiation that reached the Earth cooled the far North, displaced the Intertropical Convergence Zone to the south, and dried up the tropics. It’s plausible, but by no means proven.
In any case, the Akkadian Empire seems to have quite suddenly found itself in what we call a megadrought, meaning a drought that endures for decades.
Now, it seems that the heartland of the empire, depending as it did on irrigation, was relatively resilient in the face of sustained drying. In fact, there are some intriguing archaeological signs of adaptation. Decades after megadrought appears to have settled across Mesopotamia, engineers appear to have dug out canals across bends in the Tigris and Euphrates rivers. These canals made the flow of water more predictable, controllable, and useful for irrigation and transportation.
When complete, the canals may have counteracted any reduction in the flow of the rivers that might have been caused by lower snowfall in the mountains. If so, they were interventions that mitigated the effects of climate change in an environment. The rivers had been, to some extent, turned into machines that could be managed and fine-tuned when drought made them less efficient engines for growing food. This was a power beyond anything humans had been able to exert in the Pleistocene or early Holocene.
The trouble was that the Akkadian Empire had expanded into northern Mesopotamia, to encompass vast territories that relied on rain-fed farming. You see, where irrigation took root around the Bronze Age world, small zones of highly productive, irrigated land were islands in bigger regions of rain-fed agriculture or pastoralism, which in turn were surrounded by even bigger territories where people hunted and foraged.
And although irrigation produced more food per acre than farmland that depended on rain, there was so much rain-fed farming that the Akkadian empire still seems to have relied on grains that were grown there – not to mention the tax revenue that locals sent south. And when the rains faltered, the crops no longer grew, and the taxes could no longer be collected.
Radiocarbon dating suggests that the urban centers of Hamoukar, Mozan, Tell Leilan, Tell Brak, and Tell Mohammed Diyab – critical hubs in the northern, rain-fed territories of the Akkadian Empire – were all abruptly abandoned soon after the beginning of the 4.2 ka BP event. Buildings and fortifications that were under construction seem to have been deserted, and never finished.
In Tel Leilan, decades of excavation have painted a particularly disturbing picture. Tablets, pottery, measuring tools – all are left in place, as though people suddenly vanished where they stood. And a layer of windblown silt covers the artifacts and buildings.
It’s a vision of the ultimate climate catastrophe. Actually, it’s something from my nightmares: a city consumed by drought and dust, abandoned by panicked refugees.
Now, it’s not easy to pin down how the apparent abandonment of the Akkadian Empire’s northern cities might have destabilized the empire as a whole. After all, we don’t know the extent to which the empire depended on the grain grown in its northern territories, not to mention those taxes. We do know, however, that the empire disintegrated soon after its northern cities were deserted.
And it seems that pastoralists – herders – on the Khabur Plains, north of the collapsing empire, also suffered. Drought appears to have made the plains inhospitable for herds of animals, so pastoralists moved into southern Mesopotamia before and after the empire’s fall.
It was to resist the migration of pastoralists that the Ur Dynasty, which picked up the pieces of empire in southern Mesopotamia, built the Wall of the Martu. But like just about every wall in history that was built to keep out migrants and refugees, in the end, the Wall of the Martu seems to have failed. The migrants kept coming, and – now sedentary – eventually assumed control of the cities of southern Mesopotamia.
Eventually, the droughts faded. And Bronze Age empires, ruled by Goliaths, waxed and waned across Mesopotamia for another millennium.
Collapse. It just might be the scariest word in archaeology, history – and the study of climate change.
But when it comes to the collapse of societies, of civilizations, what does it mean, exactly?
Well, definitions differ. But most involve an abrupt and durable depopulation, a removal or replacement of elites, a decline in political and economic complexity. Settlement patterns might change, trade might be destroyed or rerouted – there’s just a fundamental rupture in the history of a people, and what was lost is never restored.
Now, some dispute the very notion of collapse in history. Of course, it’s clear that complex societies changed, often dramatically. But can archaeological and historical evidence – and even natural archives – really tell us about anything more than the fate of elites, the 1%? Can we know for sure that people died, rather than moved? If cities were deserted but their rural hinterlands flourished, is that truly a disaster?
Can we pin down when an existing order fell apart? And if a decline took centuries to unfold, would people have even been aware of it? Can we call it a collapse?
So, it’s hard to establish how, when, and even whether societies and populations collapsed in history.
But Goliath may be a different story. Goliaths – systems of political and economic domination – do seem to have crumbled. Maybe because they were cursed, as Luke Kemp puts it, by the inequalities they created, by their need to expand and to control resources in intricate networks that could come apart when stressed. Goliath looked invincible, but its foundations were less stable than they appeared.
If Kemp is right, it’s no coincidence that the first really big Goliath appears to have disintegrated in what may have been the worst drought of the Holocene.
Many died. But ordinary people tend to fare better after Goliath is slain – at least those who survived. Skeletal evidence suggests that, in one time and place after another, the health and perhaps the wealth of commoners goes up when the systems that oppress them vanish. At least until the next Goliath takes over.
The 4.2 ka BP event revealed that complex societies, states, and Goliaths responded very differently to climate change than the small communities that had dominated human history until then. It showed that these new ways of organizing people could be vulnerable to long-term trends in precipitation or temperature.
But it also demonstrated, once again, that peoples and cultures are resilient. Because, after decades and centuries of drought, the people of Mesopotamia endured. Complex societies between the Tigris and Euphrates rolled on to new glories – and horrors.
This is our season 3 finale, so I’d like to offer some reflections on the history we’ve covered over this entire season.
Time is compressing. In our first season, we explored some 45 million years of history. In our second, about 100,000 years. And now, in this third season – maybe seven or eight thousand.
What’s going on? Well, we have a lot more and more precise – or to use that word again, higher resolution – evidence for times that are closer to our present. That’s partly why there’s often more to say about shorter but more recent timespans than longer and more ancient ones.
The human story in the early and middle Holocene also is just bigger than it was in the Pleistocene. There are more people alive at any one time, doing more and more diverse and unprecedented things. Indeed, history is beginning to accelerate, with the pace of change much faster than it was in the Pleistocene.
Actually, I think we had more to talk about in the seven, maybe eight thousand years of this season than we did in the millions of years we followed in our first season. There’s a lot we couldn’t get to, and that’s partly why our next season will begin midway through the Holocene.
What’s the biggest reason that the human story accelerates in the Holocene?
It’s agriculture. You see, agriculture might well be the most important invention in human history. It didn’t make life better for most people. It was not adopted by every culture. It was even abandoned by some populations. Its debut wasn’t a simple or straightforward story of progress for our species.
But eventually, it emerged independently in one region after another. It spread across the Earth. And in time, it did change everything.
The human population increased only incrementally in the roughly 300,000 years from our evolution through the dawn of the Holocene. After agriculture, it rises from no more than five million people to about a billion when, in the late eighteenth century, the next big revolution – industrialization – emerged in Britain.
Human populations were divided and stratified in agricultural populations as they never were before, but they were also centralized – thanks to Goliath. That’s partly why agriculture wasn’t necessarily a leap forward for our species.
But it can’t be denied that innovations ultimately linked to agriculture unlocked new possibilities for people to preserve and build on knowledge. These possibilities transformed our species into something truly new in the history of life on Earth, something capable of transforming the Earth itself.
And agriculture became the most important way we undertook that terraforming project. Over thousands of years, the world’s diverse and complex ecosystems gradually gave way to carefully managed, unstable and simple ecosystems that served a single purpose – to sustain our growing numbers. Much of the land on our planet now constitutes a vast machine that continues to expand, and continues to consume the non-human Earth.
The advent of human agriculture may be the most important thing that has happened to this planet, at least since the asteroid impact that wiped out the non-avian dinosaurs. It created societies that responded very differently to climate change than any population had before. And it nourished societies that could, in time, change the climate themselves.
You and I are alive because our ancestors invented agriculture. The same is true for everyone we know. Our way of thinking and perceiving the world depends on millennia of culture that wouldn’t have existed without agriculture.
So – what do you think? Was it worth it?
In our next season, we’ll continue to think about those questions. We’ll trace the rise and decline of agricultural societies from Egypt to China to the Yucatan Peninsula. In the process, we’ll travel through the ancient world and end with the fall of Western Rome.
Climate changes were not as extreme in this period as they were in the Pleistocene, or even the early to middle Holocene. But as we’ll see, societies of unprecedented size may have been more vulnerable to them than the smaller populations that once dotted the Earth.
Climate change therefore shaped human history in the late Holocene, just as it had for 300,000 years.
For Teachers and Students
Review Questions:
- How did bronzeworking transform agricultural societies?
- What is “Goliath,” and what conditions seem to allow it to grow?
- What was the 4.2 ka BP event, and how do we know about it?
- Why is collapse difficult to identify in history?
Key Publications:
Bini, Monica et al. “The 4.2 ka BP Event in the Mediterranean region: an overview.” Climate of the Past 15:2 (2019): 555-577.
Helama, Samuli. “The 4.2 ka event: A review of palaeoclimate literature and directions for future research.” The Holocene 34, no. 9 (2024): 1408-1415.
Kemp, Luke. Goliath’s Curse: The History and Future of Societal Collapse. London: Viking, 2025.
McNeill, John R. The Webs of Humankind: A World History, Second Edition. New York: Norton, 2024.
Middleton, Guy D. Understanding Collapse: Ancient History and Modern Myths. Cambridge University Press, 2017.
Silver, Minna. “Climate Change, the Mardu Wall, and the Fall of Ur.” In Fortune and Misfortune in the Ancient Near East, edited by Małgorzata Sandowicz and Olga Drewnowska. Eisenbrauns, 2017.
Weiss, Harvey. “4.2 ka BP Megadrought.” In Megadrought and Collapse: From Early Agriculture to Angkor, edited by Harvey Weiss. Oxford: Oxford University Press, 2017.
Video and Audio Credits:
Audio: AIVA, Podbean, LALIA.
Video: Runway.
Funding provided by Georgetown University’s Earth Commons.
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