Last month’s column offered some general thoughts on how science fiction writers go about inventing plausible worlds, drawing heavily on the ideas of two masters of the process, Poul Anderson and Hal Clement. Now I want to offer some specifics showing how I devised my own best-known imaginary world, the planet Majipoor of Lord Valentine’s Castle and its various companion volumes.

I began with nothing more than the skeleton of a plot involving a dispossessed monarch and the desire to set my story on a giant world rather like the one that Jack Vance envisioned in his 1952 novel, Big Planet. I intended, though, to carry the investigation of that world far beyond what Vance had chosen to do in that one relatively short book.

Big Planet takes place on a planet with a climate somewhat like India’s that is divided into hundreds or thousands of independent principalities. Because its crust is devoid of the heavier elements, Vance’s planet has “no metal, no machinery, no electricity, no long distance communication.” Therefore —despite its immense size, with a circumference seven or eight times that of Earth—Big Planet is a low-density world with a gravitational pull about the same as ours and a similar atmosphere, thus making possible human settlement.

Vance’s novel is a lovely colorful romp. But, because SF books in the 1950s had to be fairly brief, it’s only about fifty thousand words long, and merely nibbles at the infinite complexity of the planet on which it is set. Had he wished, Vance could have placed another dozen novels there without exhausting the territory. The only time he did return to Big Planet, though, was in the relatively minor novel Showboat World, so the notion came to me of creating a Big Planet of my own and exploring it more fully than Vance did his.

At first, for the sake of distinguishing my world from the tropical jungle wilderness of Vance’s book, I envisioned a single tremendous city spreading thousands of miles in all directions, covering most of the land mass—the very opposite of Vance’s concept. (Reaching for opposites is a good way to find story ideas.) But very quickly I saw the impossibility of that. If I wanted a population of many billions, I would need extensive agricultural zones to support it; and if I wanted (as I very much did) to create a host of fascinating plants and animals, I would have to have a variety of wild places.

So pole-to-pole urban development made no sense, and in the end I fell back on a model that was even more like a giant India than Vance’s planet: a place of teeming cities surrounded by vast farming districts, and yet, nevertheless, having huge wilderness areas ranging from torrid desert to lush jungle to snow-capped mountains, surrounded by an ocean so enormous that no expedition had ever succeeded in crossing it. What I had in mind, in other words, was a planet so large that it could encompass a host of varying environments—jungles, interminable swamps, arid plateaus, great rolling savannas, rivers seven thousand miles long, cities of thirty billion people—without any sense of crowding whatever.

The astrophysical details didn’t require much homework. Since I was beginning with the assumption that my planet had to be a comfortable one for human settlement, I needed a main-sequence G-type sun much like our own. (For a touch of exoticism I made it golden-green in color rather than yellow.) The planet’s low-density structure accounted for a gravitational pull about like Earth’s despite a much greater diameter. For human use the atmosphere had to be something close to Earth’s 78-21 nitrogen-oxygen mix. By way of encouraging agricultural productivity I gave it a relatively minor axial tilt, thus avoiding sharp seasonal changes: some parts of Majipoor would be fairly dry, others rainy, but the climate would be benign everywhere except in the snowy polar regions.

Still, by employing the Vancean low-density planetary model, with its concomitant shortage of useful metals, I would have to veer somewhat from a strictly science-fictional mode of thinking, because without metals there could be very little in the way of machinery—no aircraft and no telecommunications system, for example. How, then, could I justify the existence of those cities with thirty billion people in them, with no rapid transit, no telephones, no elevators, indeed no high-rise structures? How could there be any sort of coherent central government, let alone the hierarchical and quasi-feudal monarchy that would justify a title like Lord Valentine’s Castle?

I began to see that I would have to operate on that blurry borderline where science fiction shades into fantasy: a dollop of telepathy here and there for communication, a certain amount of vagueness about technology (an ancient civilization that has long ago used up its sparse metals and forgotten how its own mechanisms work), and some kind of ground-effect vehicles (“floaters”) that didn’t require internal-combustion engines or electricity to drive them. The lack of air transport, I figured, would work in my favor, adding to the sense of planetary immensity that was one of my primary goals: on Majipoor it would take just about forever to get from anywhere to anywhere. Distant cities would become misty, quasi-mythical places.

I interject herewith that everything I have to say here about building worlds for science fiction novels applies just as well to fantasy. I regard science fiction as just one sub-set of fantasy, anyway. Everything in a fantasy novel, however it may contravene the laws of nature as we understand them, needs to have its own internal consistency, since, without the rigor of internal logic, plot problems can be trumped in any old arbitrary way for the writer’s convenience and the narrative line will quickly collapse as one rabbit after another is pulled from the auctorial hat. So the writer needs a thorough understanding of how our own world’s non-technological societies actually worked, and needs to follow those workings in all details save only the one speculative departure that generates the fantasy element itself. For further information on constructing fantasy worlds, I commend to you another Poul Anderson essay, “On Thud and Blunder,” recently republished on the Internet and easily findable there.

While the planet itself was taking shape in the forefront of my mind, other cerebral areas were quietly at work devising an elaborate plot, characters to enact it, a history and a culture and a political system, and all those other features that a lengthy science fantasy novel needs. But most of my conscious attention at that point was going toward envisioning Majipoor: its climate, its native lifeforms, above all its geography and topography. These things, I knew, would determine many aspects of the story itself, from the form of government to the movements of my protagonists.

All right: maps, next.

I drew some quick sketches. Three continents, each far larger than any of Earth’s. One, the earliest to be settled and immensely populous, to be the center of the world government; another, not as thoroughly urbanized, though with some major cities and a river of phenomenal size cutting across it, to be the home of the surviving aborigines who would, I already was coming to see, play a key role in the plot; the third, more obscure, a forbidding desert land in the torrid south.

By now I had put some meaning behind the title that had spontaneously offered itself. The eponymous Castle was the seat of the monarch, and I would put it atop a special geographical feature: a super-Kilimanjaro, a mountain thirty miles high in the middle of the primary continent. Castle Mount, I called it. It would be virtually a continent in itself, albeit a vertical one, protected from high-altitude forces of wind and cold and by weather-altering and atmosphere-creating machinery designed and installed when Majipoor still was in its technological era. There would be fifty spectacular cities along its slopes and a gigantic Gormenghast-like royal castle at its summit.

But, since the political structure of Majipoor and the plot of the novel now were unfolding in my mind with the same swiftness as the geographical background, I needed a second capital also, for I intended a double monarchy. In order to sustain Majipoorhuge population under a single stable government, I wanted a ruling system that would provide a long series of enlightened monarchs. Hereditary rule wouldn’t do that—sooner or later it gives you a Caligula or a Nero—and neither, as I see it, would democracy. (Hitler was a democratically elected Chancellor.) But I remembered the system of adoptive emperors that produced the most successful period in the long history of the Roman Empire, each ruler choosing the most qualified man of the realm to follow him to the throne and adopting him as his son: Nerva picking Trajan, Trajan Hadrian, Hadrian selecting Antoninus Pius and simultaneously designating the promising young Marcus Aurelius to be Antoninus’ ultimate successor.

I proposed—fantasy, again—to ask the reader to believe that such a system could be kept going for thousands of years if each emperor gave proper care to his choice of a successor. But also I intended to have two rulers in office at once, much as Fifth Republic France has a President and a Prime Minister, and the later Romans operated with an Augustus and a Caesar as senior and junior emperors. The older monarch—the Pontifex, I called him, with a nod to Rome—would live out of sight, in the deepest levels of a labyrinthine underground city thousands of miles south of the Castle. The junior king—the Coronal—would be the highly visible occupant of the Castle atop the great mountain, the public figure carrying out the orders that emerged from the hidden emperor in the Laby-rinth. Upon the death of the Pontifex, the Coronal would take his place in the gloomy subterranean capital and his designated successor, technically his adoptive son, would become Coronal at the Castle.

I realized at this point, also, that what I would be writing was a novel of quest, of internal discovery, of the attainment of responsibility. One should never become so obsessed with the world-building process that one loses sight of the story-building process: the two should grow simultaneously, organically intertwined, once the basic groundwork has been established. A quest-novel, then. But who would undertake the quest, and what would he be seeking? The world I was designing had taken its essential form; it was time to establish the characters who would act out the story I intended to set on that immense planet.

And I see that this is going to take another column to finish the job.