Expanding Networks of Exchange and Encounter
1200 BCE - 500 CE
This Big Era and the Three Essential Questions
In Big Era Three, humans in several parts of the world began to produce food, adopt
new forms of social organization, and interact more intensively with one another over
longer distances than in any earlier times. In Big Era Four those patterns continued,
though at a faster pace. World population continued to increase in the first millennium
BCE, though it leveled off in the early centuries CE. More cities appeared. States, which
first emerged in Big Era Three as a way of organizing large populations under a single
governing authority, now appeared in new forms that were bigger, more complex, and
more efficient at collecting taxes from the population.
Interregional systems of communication allowed goods, technologies, and ideas to
move, sometimes thousands of miles. Interlocking networks of roads, trails, and sea
lanes connected almost all parts of Afroeurasia and, in the Americas, extensive areas
of Mesoamerica and the Andean mountain spine of South America. Among the ideas
transmitted along these routes were new belief systems, which invited peoples of differing
languages and cultural traditions to share common standards of morality and trust.
Humans and the Environment
We might argue that compared to today, when humans are expending huge amounts
of energy to shape the physical and natural earth to their own purposes, Big Era Four was
not a period of drastic environmental change. That, however, is a relative matter. If we
compare that era to the three earlier ones, it is clear that humans were extracting energy
from nature and from the earth's outer crust at an accelerating pace. This intervention
produced rising agricultural productivity in the world as a whole and, for some, a higher
standard of living.
Recall that in the essay on Big Era Two, we introduced the concepts of extensification
and intensification. In Big Era Four, intensification involved human groups introducing
both farming and pastoral nomadism in parts of the world where only foragers, if any
humans at all, had previously lived. With the establishment of farming or herding in
those regions, the size, density, and complexity of social groups grew significantly. Those
places included southern Africa, the grassy steppes of northeastern Eurasia, the Yangzi
River valley in China, parts of Oceania (the Pacific Islands), Mesoamerica, and Andean
New tools and techniques that made those developments possible included improved
hybrids of food crops and in Afroeurasia more extensive exploitation of horses and
camels as work animals. Perhaps the single most important invention of the era was the
technology of iron production. Beginning late in the second millennium BCE, people
in both Southwest Asia and East Africa, independently of each other, acquired the
knowledge of how to smelt iron and work it into useful objects. This technology rapidly
spread across most of Afroeurasia.
Consequently, farmers wielding iron axes, hoes, spades, and plows opened millions
of acres of virgin land. City artisans used iron hammers, chisels, and saws to erect
great buildings of wood and stone. And monarchs increasingly armed soldiers with
iron weapons and armor. In other respects, we cannot really argue that Big Era Four
was a time of great technological change in the world as a whole. Many of the most
fundamental inventions, such as the wheel, the technology of pottery-making, or the
horse harness, had already appeared. And basic inventions did not necessarily spread worldwide. Iron metallurgy, for example, did not reach the Americas, Australia,
or Oceania in this period.
One fundamental development closely linked to the expansion of agriculture
was population growth. Between 1000 BCE and 1 CE, world population appears to
have risen from about 120,000,000 to 250,000,000. The rate of growth also went up.
Between 3000 and 1000 BCE, it took about 1,600 years for world populations to double.
Between 1000 BCE and 1 CE the doubling time was
less than 1,000 years.
One cause of human biological success in the
first millennium BCE may have been that in regions
where people regularly interacted with one another,
they slowly built up shared immunities to infectious
diseases. This would especially have happened in
densely populated regions like Southwest Asia,
northern India, or northern China. Stronger natural
immunities reduced mortality from recurring
epidemics, permitting populations to grow at a faster
rate. However, if some new infectious malady entered
a region from afar, a severe epidemic might break out
and populations take a plunge.
Environmental Impact: The Fate of Forests
As populations grew, so did their impact on the environment. Though the pace of
deforestation in Big Era Four may have been minor compared to the twentieth century,
it appears to have greatly accelerated compared to earlier times. Clearing forest cover
for fuels, farming, or grazing meant that more people could live on a given area of land.
Over the long run, however, forest cutting produced soil erosion, chronic shortages of
wood fuel, periodic famines, and extinction of some local animal and plant species.
Deforestation and the burning of trees, as well as wet rice farming, may even have begun
to alter global climate.
We have sound archaeological evidence that in Big Era Four farmers cut or burned
forests on a substantial scale in the Mediterranean basin, western Europe, East Africa,
the Ganges River valley, China, and other regions. In Mesoamerica and the Andes
Mountains, societies had neither iron tools nor large work animals until much later in
history. In both those regions, however, land clearing proceeded steadily because those
societies learned to deploy human muscle power on a large scale and very efficiently.
Humans and Other Humans
The doubling of world numbers in Big Era Four, coupled with increasing density
of farming populations, meant that in many places humans had no other choice
but to experiment with new ways of organizing their social, economic, and cultural
relations. For one thing, many more humans lived in cities at the end of this era than at
This does not mean that anything close to a majority of people inhabited cities or
that urban growth was steady and uninterrupted. Urban populations rose and fell. In
fact, cities appeared and disappeared, in connection with regional or local changes in
agricultural production, long-distance trade, infectious disease environments, political
conditions, and other factors. The table below tells us something about the general
patterns of global urbanization between 1200 BCE and 500 CE.1
Number of largest cities
Size of largest cities
Total population of largest cities
We can see here that urbanization rose steadily up to the second century CE, then
declined in the following 400 years. We can definitely link the upswing to the appearance
of several large states and empires, all of which accumulated sizable agricultural,
mineral, and commercial wealth. The
downswing after the second century CE
may be partly connected to pandemic disease
outbreaks, the decline of large empires, and
extended economic recessions in the major
The Multiplying of Cities
In Afroeurasia, cities grew and multiplied
partly because they developed increasingly strong commercial ties with one another,
sometimes across long distances. About 100 CE, the world's two biggest cities were
almost certainly Rome, with a population nearing one million, and Luoyang in China's
Han empire. The urban downswing that occurred from the third century CE was
certainly related to the decline of the Han and Roman empires.
Most cities of Big Era Four were multifunctional, serving as centers of government,
religion, trade, manufacturing, education, and artistic display. In some cities, such as
Rome or Alexandria (in Egypt), all these functions operated simultaneously. Other cities
had more specialized purposes, for example, towns of the Mediterranean coast or Inner
Eurasia, which functioned chiefly to transship goods along routes of trade.
A stretch of the Roman Empire's elaborate road network south of Rome.
Archaeologists studying the ancient Americas in recent decades have pushed evidence
urbanization further and further back in time. Along a thirty-mile stretch of the
Peruvian coast known as Norte Chico, researchers have surveyed as many as thirty small
cities, some of them founded no later than about 3200 BCE. The oldest of these centers
predates the appearance of cities anywhere in the world except Sumer in Mesopotamia.
The contours of a complex society governed by an aristocratic minority comes into clearer
view at the ruins of Chavín de Huántar, a center for ritual practice and pilgrimage
whose construction began around 800 BCE in the Andean highlands of northern Peru.
The earliest city we know of in Mesoamerica emerged about 1350 BCE in the tropical
lowlands that border the Gulf of Mexico. This center, known by its ruins as San Lorenzo,
featured an artificial central platform 150 feet high and two-thirds of a mile on each side.
This city and others that followed in the region developed in association with the early
Olmec (Olmeca) society.
These centers may have
been the earliest places
in the Americas where
an aristocratic minority
exercised some type of
over the common
population of farmers,
artisans, and hunters.
By 600 CE, the city
of Teotihuacán in
the Valley of Mexico
(the region of modern
Mexico City) may have had a population of more than 150,000, making it one of the top
ten largest cities in the world at that time.
States of unprecedented size arose in Big Era Four partly because of new technologies
that permitted rulers to extend their systems of central command farther and farther away
from their capitals. One of these advances was the perfecting of horse riding. All across
Afroeurasia, armed cavalry, which could operate on almost any terrain, replaced chariots
as an instrument of military conquest and control. Soldiers, as well as state messengers
and envoys, could transmit political orders and vital news by horseback faster than any
Other innovations that contributed to imperial growth were advanced road
construction (the Persians and Romans), canal building (the Chinese), and the emergence
of the dromedary camel as the principal transport animal in arid lands from Africa to
Below is a table of the three biggest empires of the 1000 BCE to 500 CE period.
Their land area is compared to that of the continental United States.2
Approximate size in square miles
Achaemenid Persian empire
Continental United States
These ancient states were empires not only because they were big but also because a
single government, and an elite class of particular origin (Han Chinese, Indo-Iranian-speaking Persians, Latin-speaking Romans), ruled over peoples of diverse linguistic,
ethnic, and religious identities.
In Big Era Four, the majority of the world's people probably did not live within
the frontiers of empires. Some lived in city-states, which were relatively small
sovereign territories centered on a single city. Greek and Phoenician city-states of the
Mediterranean are obvious examples. Many other people lived under no state authority
but in societies organized in kinship groups.
Nevertheless, a sweeping view of Afroeurasia at about 100 CE reveals a nearly
continuous chain of states, most of them gigantic, extending from the Atlantic to
the Pacific. All these states enjoyed extended periods of political order and economic
prosperity, and those conditions in turn stimulated long-distance exchanges of products
and ideas, not just within states but between one another.
In Big Era Four, especially between about 300 BCE and 300 CE, merchants,
shippers, camel drivers, and sea captains extended and strengthened trade routes across
Inner Eurasia on the silk roads, the basins of the Mediterranean and Black seas, and the
Indian Ocean. And the last centuries of the era also saw the beginnings of camel caravan
trade across the Sahara, linking peoples of tropical Africa to the Mediterranean rim.
The Shape of Societies
In Big Era Four the vast majority of the world's population were farmers, herders, or
foragers. They subsisted on their own production, and they lived short lives compared to
today. However, more and bigger cities, plus the rise of states that concentrated immense
amounts of wealth, led to sharper distinctions of social class between elite minorities that
held wealth, power, and privilege, and everyone else. In urban societies there might have
also been a sizeable class of merchants, artisans, scholars, and other people with special
skills who accumulated substantial wealth, though not necessarily much political power
At the bottom of the social scale were slaves. There is no doubt that this era witnessed
a huge expansion of slavery and organized slave trade in many parts of the world, notably
the Mediterranean basin. For example, the slave population in the central part of the
Roman empire at the end of the first century BCE may have been as much as 40 percent
of the total population.
In all the urbanized societies of Big Era Four, adult males dominated political and
social life, as far as we know. One would have to visit forager, pastoral, or small-scale
farming societies to find reasonably egalitarian relations between women and men in
daily life. In the big states and empires, women at the very top of the social ladder appear
to have enjoyed, relatively speaking, the greatest freedom to come and go, accumulate
property, and influence political affairs.
Humans and Ideas
The system of writing that emerged in Afroeurasia in Big Era Three greatly enhanced
the speed and range of collective learning among humans. Those writing systems,
however, were logographic. That is, they employed signs, or characters, that represented
meanings. Therefore, they required thousands of separate signs (written characters), each
having a specific meaning. This kind of writing system had the advantage of allowing
people to express meanings in very precise, subtle ways.
The new development in Big Era Four, however, was the appearance of the earliest
alphabetic writing systems. The signs used in them represented, for the most part, sounds
of speech, not meanings. Meanings may be expressed in millions of ways, but the number
of sounds humans can make with their lips and tongues is drastically limited. Alphabetic
systems, therefore, relied on a small number of signs (for example, 26 in the English
alphabet, 28 in the Arabic one). Nevertheless, these signs could be arranged in countless
ways to represent the nuances of human thought.
The earliest alphabetic system that we know of appeared in Southwest Asia near the
end of the second millennium BCE. In the following centuries variations of that system
spread from the Mediterranean basin to India. People could master alphabetic systems
faster and easier than logographic ones. Therefore literacy spread rapidly in Big Era
Four, though especially among scholars, priests, officials, and merchants, not ordinary
farmers and workers. Nor did alphabetic systems completely replace logographic ones.
The Chinese character-based system is the leading case of modern logographic writing.
Another development of Big Era Four, and one related to the spread of writing, was
the appearance of several belief systems that embraced people of differing languages and
cultural traditions, what we often call "world religions." The great majority of people
in that era practiced local religions, that is, systems that centered on local gods and
goddesses, sacred places in nature, astrology, magic, and pronouncements of shamans—
individuals who mediated between the natural and supernatural worlds. In large states
and empires, religious life tended to be diverse, though rulers could seldom resist
encouraging their subjects to think of them as individuals with supernatural powers or
even as divine beings. For example, when the Roman state made the transition from a
republic to a sprawling autocratic empire, its leaders were transformed from ordinary
mortals into gods.
Since people do not appear to have lacked for religious life on a local scale from very
early times, why did several large-scale belief systems emerge in Big Era Four? In fact,
why did all the major world religions appear in that era, with the exception of Islam?
One possibility is that by about the middle of the first millennium BCE, Afroeurasia
reached a level of population and an intensity of commercial and cultural interchange
that required larger systems of morality and shared belief. The new religious systems
provided foundations of cultural communication, moral expectation, and personal trust
among people who were meeting, sharing ideas, and doing business with one another far
beyond their local neighborhoods. The new belief systems, however, were by no means all
the same. Each one offered distinctive answers to persistent questions about the human
condition and different ways of approaching worship, ritual, and communal life. The table
below provides some basic information about new religions that appeared in Big Era Four.
Time of appearance
5th century B.C.E.
1st century C.E.
5th century B.C.E.
5th century B.C.E.
early 1st millennium B.C.E.
early 1st millennium B.C.E.
Buddhism, Christianity, Hinduism, Judaism, and Daoism all offered paths to
self-transformation and to eternal salvation in one form or another. Christianity and
Judaism were the most firmly monotheistic, proclaiming one omnipotent and omniscient
god. Hinduism made room for numerous, powerful gods and goddesses. Buddhism
and Daoism also accepted the existence of multiple divine beings in various forms
and incarnations. Like Christianity and Judaism, however, Buddhism, Daoism, and
Hinduism envisioned a unitary, all-encompassing cosmic reality.
Buddhism and Christianity emphasized their universalism and appeal to all humans,
and both spread widely across ethnic and linguistic frontiers. Judaism remained closely
identified with the Hebrew people and their descendants, though by the end of Big
Era Four a diaspora of Jewish communities extended nearly across Afroeurasia. All six
systems taught that human relations should be guided by kindness, selflessness, and
decency. Confucianism, which some scholars characterize as an ethical system rather
than a religion, particularly emphasized public moral behavior, good government, and
These six systems may of course be compared and contrasted in numerous other ways.
In terms of general beliefs and practices, none can be set rigidly apart from all the others.
Also, within each tradition, significant variations developed depending on local cultural
tendencies and social environments. For example, in the Christian tradition, several
different "churches," each with distinctive beliefs and practices, emerged during the first
or early second millennium CE. These included the Eastern (Greek) Orthodox, Roman
Catholic, Arian, Nestorian, and Ethiopian churches. In Afroeurasia the only major belief
system that did not appear in Big Era Four was Islam, which came on the scene in the
seventh century CE.
All these belief systems had philosophical aspects in the sense that they encouraged
investigations into the structure and meaning of the physical and natural universe. None
of them was incompatible with types of inquiry and speculation that we associate with the
beginnings of science. In the Aegean Sea region, for example, Greek-speaking scholars,
whose religion in the first millennium BCE embraced a large household of deities,
developed a method of scientific and moral questioning known as natural philosophy.
According to Hellenism, the system of thought and creativity based on Greek language
and culture, human reason could be applied to developing general theories to explain
natural, cosmic, and psychological phenomena. These thinkers saw no contradiction
between efforts to detect universal patterns in nature and their conviction that the gods
fundamentally ruled it.