How the traction cities and towns of Mortal Engines work
First of all, let us not go full Star Wars nerd level on the mechanics of how the traction engines of Mortal Engines actually work.
Yes, the idea of whole cities crawling across the Earth for thousands of years is absurd if you hold it up to real-world engineering. So is the brutal civic religion of Municipal Darwinism, where moving cities hunt, consume, and dismantle each other in the name of survival.
But that is the trick of Philip Reeve’s world. It is not meant to be a sensible transport policy. It is a satire, a nightmare, and a giant rusted metaphor with teeth.
So, for a moment, we accept the impossible and suspend our belief. We accept that traction cities such as London work.
We accept that they are vast mechanical beasts, kilometres wide, carrying entire societies inside their metal shells...
Why were traction cities built?
Traction cities were built after the Sixty Minute War destroyed the Earth and left vast stretches of the planet damaged, unstable, poisoned, or simply too dangerous to settle in the old way.
The basic idea was practical at first. If the land was ruined, then the surviving human population would need to move. Not migrate once, but keep moving. Towns and cities became engines. Civic life became mobile. Survival became mechanical.
The prequel novels, beginning with Fever Crumb, show how this world began to take shape under Nicholas Quirke, drawing on ideas associated with Auric Godshawk. What begins as an answer to collapse eventually mutates into a whole civilisation built around motion, hunger, and conquest.
That is the important point. Traction cities were not only invented as machines. They became an ideology. Once people were taught that a city must move to live, it was a short leap to the uglier belief that a city must eat to live.
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| Medusa. |
What is a traction city?
A traction city is a mobile settlement built on wheels, caterpillar tracks, engines, furnace systems, fuel stores, and vast internal machinery. The largest are tiered metropolises, stacked upwards like industrial wedding cakes, with the richest and most powerful citizens living near the top while the smoke, labour, noise, and filth collect below.
London is the great example in Mortal Engines. It is not merely a city that moves. It is a predator city, built to chase smaller settlements, swallow them, strip them for parts, and use their people, metals, fuel, food, tools, and Old-Tech to keep itself alive.
Not every mobile settlement is the size of London. Some are towns. Some are villages. Some are tiny hamlets with modest engines, sails, improvised wheels, or crude propulsion systems. The world of Mortal Engines is full of strange moving communities, from grand predator cities to desperate little settlements trying not to become someone else’s dinner.
| Type of settlement | How it survives | Place in the food chain |
|---|---|---|
| Great predator cities | Hunt smaller cities and strip them for resources. | At the top, until fuel, politics, or bigger powers catch up with them. |
| Medium cities and towns | Hunt weaker towns, trade when possible, flee when necessary. | Both predator and prey. |
| Villages and hamlets | Move lightly, hide, scavenge, trade, or rely on luck. | Usually prey. |
| Static settlements | Remain fixed and often oppose the traction city system. | Targets for predator cities and symbols of Anti-Tractionist resistance. |
How does London’s society work?
London models itself on a warped version of Victorian society. It has ceremony, class, hierarchy, guilds, uniforms, civic pride, and the comforting myth that London’s hunger is somehow noble because London is London.
Its society is divided into major guilds and smaller professional orders, each helping the city function as both a metropolis and a machine.
The Guild of Engineers
The Engineers maintain the machines that keep London alive. They control the engines, systems, furnaces, weapons, and dangerous technological projects buried inside the city. In practice, this gives them enormous political power because whoever controls the machinery controls the future of the city.
By the time of the original novel, London is ruled by Magnus Crome, the Lord Mayor and head of the Guild of Engineers. His authority shows how easily civic government and technical control blur together in this world.
The Guild of Historians
The Historians collect, study, and preserve Old-Tech, much of it dangerous, misunderstood, or treated with a kind of religious awe. Chudleigh Pomery belongs to this world, as does young Tom Natsworthy, who begins the story as an apprentice historian.
The irony is delicious. In London, history is both treasured and ignored. The city worships relics of the old world while repeating the same hunger, violence, and imperial arrogance that helped ruin the Earth in the first place.
The Guild of Navigators
The Navigators steer London and plot its course across the Hunting Ground. Their work is not just about direction. It is about survival, fuel strategy, prey selection, and avoiding landscapes or enemies that might cripple the city.
The Guild of Merchants
The Merchants run London’s economy. In a traction city, commerce is tied directly to predation. Salvage, labour, fuel, food, relics, spare parts, and captured populations all become part of the city’s internal market.
When London catches another town, the event is not merely military. It is economic. The city feeds. The markets benefit. The guilds gain new material. The citizens are reminded that Municipal Darwinism works, at least until it does not.
Why is St Paul’s Cathedral important?
At the top of London sits St Paul’s Cathedral, one of the few structures known to have survived the devastation of the Sixty Minute War.
Its position matters. St Paul’s is a symbol of continuity, authority, and old-world memory. In a city built from scavenged civilisation, the cathedral gives London a sacred crown. It tells the people below that London is not merely a machine. It is history. It is destiny. It is supposedly worth preserving at any cost.
That is why its role in the story becomes so important. The cathedral is tied directly to the secret of MEDUSA, the ancient weapon at the centre of London’s ambitions. What looks like heritage becomes concealment. What looks holy becomes part of a war machine.
How do traction cities catch their prey?
A predator city survives by hunting smaller settlements. The chase has to be fast enough to succeed, but not so wasteful that the city burns more fuel than the prey is worth. That tension sits underneath the whole traction system. Hunger drives the cities forward, but the act of feeding also drains them.
Most predator cities use structures called jaws to seize prey and pull it into the Gut. In the film version of Mortal Engines, London fires huge hooks into the smaller mining town of Salthook, then drags it backwards toward the city’s mouth. It is one of the clearest visual statements of the whole world: London does not simply conquer. London consumes.
Once captured, the smaller settlement is dragged into the Great Under Tier, where it is dismantled. Metal is stripped. Engines are broken down. Fuel is taken. Food, tools, artefacts, and people are absorbed into the greater city.
Tom Natsworthy describes the Great Under Tier as “a stinking sprawl of factories and furnaces between the jaws and control room.” That one description tells us nearly everything. The Gut is industry as digestion. It is the stomach of the city.
The brutal genius of the traction city idea:
Reeve turns urban life into an ecosystem. London has a mouth, guts, hunger, waste systems, social classes, and political organs. It is not just a setting. It is a living predator with a government attached.
What happens to captured people?
The fate of captured populations depends on the city doing the capturing. Some people are absorbed into the predator city’s lower tiers, becoming workers, servants, apprentices, or second-class citizens. Others are treated far worse.
The novels make it clear that slavery exists in this world. Cities and corporations buy and sell human beings. The Nabisco Shkin Corporation becomes one of the uglier examples in the later books, showing that Municipal Darwinism is not only about machines eating machines. It is about people turning other people into resources.
That is one reason the world of Mortal Engines has such bite. The giant wheels and roaring engines are spectacular, but the real horror is social. A whole civilisation has convinced itself that predation is natural, profitable, and morally acceptable.
How big is London in Mortal Engines?
London is 2.5 kilometres long in the movie, which gives the film version a clearer visual scale. It is massive enough to feel impossible, but compact enough to move like a single aggressive machine across the Hunting Ground.
The book version is even stranger because Reeve lets the idea breathe beyond simple measurements. London feels like a whole nation condensed into a mobile hierarchy. It has museums, slums, engine districts, elites, apprentices, religious architecture, military ambitions, and filthy industrial spaces buried beneath civic grandeur.
Why traction cities matter to the whole Mortal Engines story
The traction city is the central image of Mortal Engines. Everything else grows out of it: Municipal Darwinism, Anti-Tractionism, scavenger culture, class conflict, lost technology, imperial nostalgia, and the fear that humanity survived the apocalypse only to rebuild its worst habits on wheels.
London is not evil simply because it moves. It is dangerous because it has turned movement into faith. Its citizens believe the city must keep going, must keep feeding, must keep expanding, because the alternative would mean questioning the entire system beneath their feet.
That is why the traction cities remain such a memorable invention. They are ridiculous in the best possible way, but they are also painfully recognisable. They are empires. They are corporations. They are old powers eating the future to keep their engines running for one more day.
