I've just seen the Mortal Engines movie and I'm looking forward to reading the books. I have a question about the economics of this world that Phillip Reeve has created.

The traction city London has a population of several millions. It seems unlikely that they are capable of growing enough food to support that many people, at least using ordinary agricultural methods which require large open spaces. Yet everybody looks healthy and well fed. So where do they get their food from?

Conceivably if London eats a smaller city it could plunder whatever food it is carrying, but that would not last them long nor would it be a reliable food source. Also the captured population still needs to be fed, since according to Municipal Darwinism they are supposed to be given a chance to make a new life aboard their new unchosen "home" - and London adheres to it in practice, at least sometimes.

We know some trade does occur, but we are told that most of Europe (the Great Hunting Ground) is a wasteland of mud and caterpillar treadmarks with little vegetation, so there are probably no places where food can be grown on a scale large enough to support even one traction city.

We also know that cannibalism is not unknown, and we see people drinking an unappetising green slop made from algae, but these also don't seem to be enough to sustain the efficient, technological society that London is shown to be.

Is there an in-universe explanation for how the traction cities feed their human populations?

  • London Green is people...
    – Valorum
    Jan 2, 2019 at 20:12
  • 1
  • 1
    You can only extract so much wasted nutritional value from excrement. A more low-tech solution would be a combination pigsty and toilet - the pig eats the poo, then you eat the pig. But it can't be a closed system - you still need to get real food from somewhere.
    – Batperson
    Jan 2, 2019 at 20:20

1 Answer 1


In the novels, food production falls into three main areas; Predation on other smaller settlements (both mobile and static), the internal growing of foodstuffs and trading with other towns and cities that aren't worth attacking.

He set off at a run, and soon reached Bloomsbury Park, out in the open air on the tier’s brim. It had been a proper park once, with trees and duck-ponds, but because of the recent shortage of prey it had been given over to food production and its lawns grubbed up to make way for cabbage-plots and algae-pans.


For ten years it [London] had eaten nothing but tiny farming towns and static settlements in those wet hills. Now, at last, the Lord Mayor had decided that the time was right to take his city back over the land-bridge into the Great Hunting Ground.

Mortal Engines

Most of the characters would be on the borderline of malnutrition if it wasn't for the prevalence of spinach and easily-grown greens

There was nothing to eat in Grimsby except what the Lost Boys stole, and the Lost Boys stole only what boys who have no one to nag them about balanced diets and no-snacks-between-meals eat. Sugary biscuits, cheap, soapy chocolate, bacon sandwiches oozing grease, thin rounds of algae bread smeared thick with garish spreads, glasses of ill-chosen wine that kicked like airship fuel. The only concession to healthy eating was a tureen of boiled spinach in the centre of the table. “I always make sure the boys bring back a bit of greenstuff,” explained Uncle, dishing up. “Helps keep the scurvy at bay.” It spattered on to Tom’s plate like something dredged from a blocked sump.

There's also some element of trading for food with other (less easily attacked) cities and settlements

“It’s appalling,” agreed Nimmo. “The sort of prisoners we are being sent these days are just too feeble. If the Guild of Merchants made more of an effort to solve the food shortage they might be a bit healthier, or if the Navigators pulled their fingers out and tracked down some decent prey for once… But I think you have seen enough, Miss Valentine. Kindly ask Apprentice Pod whatever it is your father wishes to know, and I shall take you back to the elevators.”

and several "fishing cities" that seems to exist for the purpose of trading food for other materiel with land-based cities and towns.

Dun Laoghaire

A rather fishy raft city, whose claim to fame is being the birthplace of the aviatrix Orla Twombley. Ruled by powerful herring magnates, Dun Laoghaire travelled from fishing-bank to fishing-bank all over the North Atlantic, sometimes venturing as far as the Newfoundland Banks, shockingly close to the Dead Continent. It engaged in fierce rivalries with other fishing cities, and some dark rumours claim that it was Dun Laoghaire’s saboteurs rather than pack ice which caused the sinking of Grimsby.

The Traction Codex

In the film there's a machine which recycles effluent back into edible food

I found it very funny that in Scuttlebutt there was a machine in the kitchen in the background that you don't really see where food was being made out of poo. And it actually was visually moving and stuff, and I was just like, 'Who made this?' They went through with it, it's actually working, and it's not even really featured. And I was just like, 'Wow.'

Mortal Engines Has A Hidden Machine That Makes Food Out Of Poo

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