Great Cities of the World

What Is a City?

A city is a large, permanent settlement where many people live and work close together. The difference between a village, a town and a city is mostly about size — but a true city is more than a lot of buildings. It is a place where strangers meet, where goods are traded, where ideas are shared, and where many different jobs are done.

Geographers use the word urban to describe towns and cities, and rural to describe the countryside. For most of human history, the great majority of people lived rural lives, farming the land. That has now flipped. More than half of all people on Earth live in urban areas, and the share is still rising. We have become a city-dwelling species.

In this book we will explore why cities grow where they do, how some of the world's greatest cities began, and what life is like in the giant megacities of today. A city is a kind of living machine — and like any machine, it is fascinating to look inside.

Why Cities Grow Where They Do

Cities do not appear by accident. Look at where the world's great cities sit and you will notice patterns. Above all, cities grow where there is water.

A river or harbour gives a settlement almost everything it needs: fresh water to drink, fish and farmland nearby, and — most importantly — an easy way to move heavy goods. Before trains and trucks, water was by far the cheapest way to transport cargo. So London grew on the River Thames, Paris on the Seine, Cairo on the Nile, and great port cities like New York, Shanghai and Mumbai grew around natural harbours where ships could shelter and trade.

Other things draw people too. Cities spring up where trade routes cross, where there is fertile land to feed many mouths, where minerals can be mined, or where it is easy to defend against enemies. The best city locations often have several of these at once. Once a city starts to grow, it pulls in even more people, because that is where the jobs, the markets and the opportunities are.

The First Cities

The very first cities appeared thousands of years ago, in places where farming produced more food than the farmers themselves needed. That surplus was the spark. When some people no longer had to grow their own food, they could become builders, potters, priests, traders and writers instead — and so the city was born.

One of the earliest known cities was Uruk, in Mesopotamia (today's Iraq), built more than 5,000 years ago between the Tigris and Euphrates rivers. Ancient cities also rose along the Nile in Egypt, the Indus in South Asia, and the Yellow River in China — always, you will notice, beside great rivers.

These first cities gave us many things we still use: writing, written laws, large temples and the very idea of living together by the thousand. To learn more about these early peoples, the companion book The Ancient Egyptians explores one of the great river civilisations in detail.

London: A City of Layers

London, the capital of the United Kingdom, is a wonderful example of how a city grows in layers over time. It began nearly 2,000 years ago as a Roman town called Londinium, founded on the River Thames because the river was wide enough for trade but narrow enough to bridge.

Over the centuries, London survived fires, plagues and wars, and grew with each age. Medieval kings built castles and cathedrals; later, busy docks made it one of the world's greatest trading ports. During the Industrial Revolution, factories and railways pulled in millions of workers, and the city swelled outwards.

Today London is a global city of nearly nine million people, where you can hear hundreds of languages spoken in a single afternoon. Walk its streets and you walk through history: a Roman wall here, a medieval church there, a glass skyscraper next door. Many old cities are like this — not built all at once, but layered up across thousands of years.

Tokyo: The Largest City of All

If you want to see the future of cities, look at Tokyo, the capital of Japan. The Greater Tokyo area is usually counted as the largest urban area on Earth, home to well over 30 million people — more than live in many entire countries.

Tokyo shows how a megacity copes with enormous numbers. Millions of people travel each day on one of the most famous railway and subway systems in the world, where trains run so precisely that being a minute late is big news. Land is so valuable that buildings climb high into the sky and burrow deep underground, with whole shopping streets beneath the surface.

Tokyo also sits in a region where earthquakes are common, so its engineers have become world leaders in designing buildings that can sway safely when the ground shakes. It is a city that has learned to live with both the pressures of size and the dangers of nature.

Megacities and the Move to the City

Geographers use the word megacity for any city with more than 10 million people. A hundred years ago there were almost none. Today there are dozens, and most of them are in Asia, Africa and South America. Cities like Delhi, Shanghai, São Paulo, Mexico City, Cairo and Lagos have grown at astonishing speed.

Why are cities exploding in size? The main reason is migration — people moving from the countryside to the city in search of work, education and a better life. This shift from rural to urban living is one of the biggest changes in all of human history. In 1800, only a tiny fraction of people lived in cities. Today more than half do, and by the middle of this century the share will be far higher still.

This rush to the city brings opportunity, but it also brings problems that planners are racing to solve.

The Challenges Cities Face

A city that grows too fast can struggle to keep up with itself. Among the biggest challenges are:

• Housing. When millions of newcomers arrive, there are not always enough homes. Crowded, poorly built neighbourhoods can spring up on the edges of fast-growing cities.
• Transport. Moving millions of people each day is hard. Too many cars cause traffic jams and waste hours of people's lives, which is why great cities invest in trains, buses, trams and cycle lanes.
• Pollution. Factories, traffic and heating can dirty the air and water. Air pollution is a serious health problem in many large cities.
• Water and waste. A big city needs clean water piped in and dirty water and rubbish taken away — an enormous, hidden engineering effort that runs day and night.

These problems are real, but cities are also places where clever solutions are tested. Because so many people live close together, ideas spread fast, and a good idea in one city is quickly copied in another.

The Cities of Tomorrow

Around the world, planners and citizens are trying to make cities cleaner, greener and fairer. Some cities are adding parks and trees to cool the streets and clean the air. Others are building electric buses and trains, banning the most polluting cars, or filling streets with bicycles. "Smart" cities use sensors and computers to manage traffic lights, water pipes and electricity more efficiently.

There is a good reason to get this right. When people live close together, a city can actually be a very efficient way to live: shorter journeys, shared transport, and services like hospitals and schools within easy reach. A well-designed city can give millions of people a good life while treading more lightly on the planet than the same people spread thinly across the countryside.

Cities have been at the centre of human life for 5,000 years. As more and more of us become city-dwellers, the choices we make about how to build them will shape the future of the whole world.

What We Have Learned

We have travelled from the very first cities beside ancient rivers to the giant megacities of today. We saw that cities grow where water, trade and good land meet, and that great cities like London are built in layers over thousands of years.

We learned that a megacity holds more than 10 million people, that Tokyo is the largest of all, and that the world is in the middle of a huge move from rural to urban life. We also faced the real challenges of crowding, traffic and pollution — and the clever ways cities are trying to solve them.

Cities are humanity's grandest invention: messy, crowded, endlessly creative machines for living together.

Keep exploring the human world: meet the nations these cities belong to in Countries, Flags and Capitals, or find your way around them in Maps and Navigation.