Is there a reason given as to why Trantor is completely underground? Seems like would be a huge waste of space for it. I know there are 40+ billion people there, but would think a planet sized city would be more like Coruscant in Star Wars. Tall buildings and underground.

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    Using all the available space is a "huge waste of space"? How? It's not like living in a city that's all miles high towers gives you much of a sight either.
    – Luaan
    Mar 22, 2016 at 8:49
  • fair enough. I guess 'huge waste of space' was little extreme. Maybe 'inefficient' would be better. We have 8 billion on Earth, mostly above ground with mostly ocean. Trantor all land (I think). Either way, I misunderstood the book, it is not ALL underground, just no one goes outside. Mar 22, 2016 at 12:35
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    Oh, you mean how few people there are :D Yeah, it doesn't add up. The thing is, city-planets aren't thermodynamically plausible anyway, so guessing how many people can survive on a planet is a stretch no matter what you do. Also note that the Foundation series started in 1942, when the world population was only around 2 billion - 40 billions sounded a lot bigger (20x) than today (6x). And even today, most of the ground surface is not occupied by residential buildings - it's mostly agriculture. Depending on who you ask, you may get numbers as low as 0.05% for residential land usage globally.
    – Luaan
    Mar 22, 2016 at 13:06
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    Trantor has a land area of 75 million square miles, so the pop. density is ~500 per sq mile, less than Maryland or the UK. In Second Foundation Asimov retconned Trantor's population to 400 billion -- about as dense as the metro areas of Montreal or Sydney or San Francisco. That's probably too dense to feed itself, but it's not a world full of skyscrapers.
    – sjl
    Mar 23, 2016 at 6:47

4 Answers 4


Short answer, it's not all underground. "Trantor's buildings are all subterranean or under domes due to worsening weather conditions" as indicated by Wikipedia, sourced to Prelude to Foundation, pages 110 and 118. And, in the original trilogy, the city was described as being towers, closer to Coruscant's depiction.


The answer is given in Prelude to Foundation -- it's climate change. Trantor's climate deteriorated as it was developed and urbanised, to the extent that people preferred to live underground.

And Trantor itself is a bigger puzzle than almost any world. According to the records, it had a fairly normal weather pattern when it was first settled. Then, as the population grew and urbanization spread, more energy was used and more heat was discharged into the atmosphere. The ice cover contracted, the cloud layer thickened, and the weather got lousier. That encouraged the movement underground and set off a vicious cycle. The worse the weather got, the more eagerly the land was dug into and the domes built and the weather got still worse. Now the planet has become a world of almost incessant cloudiness and frequent rains - or snow when it's cold enough. The only thing is that no one can work it out properly. No one has worked out an analysis that can explain why the weather has deteriorated quite as it has or how one can reasonably predict the details of its day-to-day changes.

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    Oh hey, global warming.
    – JAB
    Mar 22, 2016 at 16:27

The opening to Foundation (where Gaal Dornick arrives on Trantor) states that everyone on Trantor is agoraphobic due to never seeing the open sky. The world-city is kilometers deep, and nobody wants windows. But its not exactly underground, its just that "ground level" has ceased to be a useful concept.

The only green space is around the Emperor's palace:

There was no green to be seen; no green, no soil, no life other than man. Somewhere on the world, he realized vaguely, was the Emperor's palace, set amid one hundred square miles of natural soil, green with trees, rainbowed with flowers. It was a small island amid an ocean of steel, but it wasn't visible from where he stood.

This implies that the climate is not so unpleasant as to prevent the Emperor from taking the air in his garden. On the other hand perhaps the garden has a transparent dome. And I wonder how he recruits gardeners, given the general agoraphobia. Perhaps he invites recalcitrant politicians out for a stroll and won't let them back in unless they agree with him.

Note: technically agoraphobia is not specifically a fear of big open spaces or open skies. The technical name for fear of falling into the sky is casadastraphobia.

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    The recruiting of gardeners is a pretty central plot concept in one of the prequel novels :)
    – SáT
    Mar 21, 2016 at 18:50

In Second Foundation trilogy is said that Trantor is analogue of The Caves of Steel of old Earth: it is insurance against New Renaissance (scientific and technological revolution which inevitably ends chaos and technophobia). It is measures taken by Daneel to protect Empire.

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