Creating a Fantasy Cosmos

Martin Rezny
Words of Tomorrow
Published in
15 min readFeb 27


Game developer’s worldbuilding journal; entry #1


In the beginning, there was a story about some characters. Then you asked yourself where the story takes place, so there was a place. Then you realized that a place must exist on a world, so there was a world. Then guess what, you figured you can’t have a world without a space to put it in. Before you knew it, you had to come up with a whole damn solar system.

For a while now, I have been one of the storytellers developing the upcoming Spellborn fantasy RPG game as part of the Sagittaras Games indie studio. If you’re interested in seeing our current progress, updates are on our reddit thread. My specialty is worldbuilding, so I decided to share some of my methods while showing what it is that we’re making.

I won’t include any spoilers for the story, don’t worry. I will describe in general terms which story problems we had to solve and how we went about doing that. Hopefully, this will be useful to other worldbuilders, both in terms of what worked and what didn’t, at least as inspiration for coming up with something else. Well, let’s put our god-creator hats on.

Something Out of Nothing

When you realize you have to come up with a whole new universe, it may feel daunting. Where does one start with that? You could go chronological, as it were, from the origin. But that way, it would take you a while until you got to the present day in your story. Not to mention that in the context of the fantasy genre, creation stories usually are supposed to be figurative.

With fantasy, it’s always a good idea in my opinion to look into history and existing mythology for inspiration, as that solves multiple problems for you at the same time. For starters, you don’t have to come up with absolutely everything yourself, and it also immediately lends the story some level of realism and immersion. Real people having believed something made-up makes made-up people believing in something similar look realistic.

Of course, in your fantasy world, something made-up can be in fact real at its core, in which case congratulations, your story is now about something. What we decided to go with as a source of inspiration was ancient to medieval cosmology and astrology. Just making a choice like this immediately points you to where to start with the cosmos building.

The word “cosmos” is already a hint. In a fantasy setting, it makes a lot of sense to have the inhabitants of the world think of objects in space as living entities, and of the space as a whole as a living organism. An organism which is analogous to and connected with all life on the world you created.

Different civilizations in our past had come up with different cosmologies and astrologies, as should you for your own fantasy cosmos, of course. This means you can choose whichever elements of existing real-world lore fit your story the best and use those, while discarding or modifying the rest, and perhaps coming up with entirely novel ideas too. It’s your world.

Unfortunately, the common level of education about something like the history and methodology of historical astrologies (plural) is basic to non-existent, even among scientists and academic scholars, so it may be difficult to find good sources of inspiration in this area. I have spent years doing my own original research, and this is what I think is good to know.

An ancient civilization likely has to develop cosmology in a certain logical order and for specific reasons. You start with what you can see in the sky. On Earth with human eyes, people of the antiquity were able to see the Sun, the Moon, and planets from Mercury to Saturn. That’s it. This means that at minimum, you should start with about seven-ish planets, plus one sun and one moon (your people wouldn’t see moons of other planets).

All that the ancient people without telescopes would know about the planets would be their luminosity, color, and path throughout the heavens, or time cycle. In fact, astrology as a practical tool is all about using the cycles of heavenly bodies for time measurement. Ancients would especially note main turning points, like solstices and equinoxes, and big, rare, flashy events like eclipses, meteor showers, comets, or distant supernovae.

Whatever celestial choices you make, however, you need to keep in mind that even if your people don’t know real astronomy or physics yet, they still likely exist. For the sake of basic realism, even if magic is real and the objects in space are intelligent beings, they should probably retain most of their realistic properties, like size, distance, orbital mechanics, and so on.

Of course, you could decide to ditch real cosmology altogether, going in the direction of something like the Elder Scrolls universe where “stars” are not orbiting spheres, but instead holes in the plane of Aetherius. Which can be cool, for sure, but with departures this large from both physics and history, you really are choosing to be on your own, creatively. But good luck to you.

We decided to take the more realistic route with Spellborn, so we created a basic solar system similar to Earth’s, with some modifications. We were considering doing multiple suns at first, but then we decided against it, as that level of departure from our normal would shift the story too far into science fiction, if we wanted to make the cosmology feel realistic. Similarly, multiple moons also raise too many overly sci-fi questions.

Besides, there’s something special about the one sun-one moon setting, some mystery and magic to it that we haven’t fully explained yet even on the level of real modern astronomy. This is the only way in which you can get perfect eclipses, assuming the size-distance ratio between the moon and the sun is just right. We decided we definitely want perfect eclipses.

So, one sun and one moon it was. With that, the main cycles that your civilizations should be using to measure time are either the solar year or the lunar year. If you want, you can make the solar year overlap in some regular way with the lunar year, which isn’t the case in our solar system. This means you need to answer how many days and how many months (lunar revolutions) are there in the year. Numbers are a bit of a big deal.

You should also think of the main way in which your civilizations measure time during the day. Historically, it was usually sun dials or water clocks, which aren’t very precise or convenient methods. Perhaps that’s a good place where to insert some magic or early technology. In any case, precise time measurement is a necessary precondition for something like an astrological ascendant, or precise time factoring into a horoscope. Before that, only sunrise, zenith, sunset, and midnight should matter.

The Magic of Numbers

Speaking of numbers and horoscopes, the modern default is the metric system in base ten, and with it, a rather arbitrary attitude toward numbers. Historically speaking, this is a major anomaly. Most cultures that have ever existed have measured time, distance, weight, and even how much money you have as parts or multiples of natural cycles, the human body, or various natural objects. You could literally measure the universe in human beings.

Interestingly, most cultures, all ten-fingered as we are, didn’t use number 10 much. To put it very simply, there is a reason why in western astrology, there aren’t 13 or 17 signs, but 12. It is likely the same reason why there are 12 or 24 hours in the day, and not 13 or 17. If what you’re doing most of the time are parts of things, or division, you’re interested in how many factors a number has. 12 is objectively better than 10, as it has more factors.

You don’t have to always default to 12 specifically, although math like this (or numerology) is so universal that it makes the exact same sense in every conceivable universe. Different numbers can be differently useful, and symbolic of different things. Depending on the particular needs of your people or their particular history, you can build your calendars, zodiacs, mythological symbolisms, and figures of speech around different numbers.

You can decide to have a faith of the seven, for example, like George R. R. Martin. That is, if you intend to keep your religion mysterious, because that’s the symbolic implication of number 7, based on how difficult it is to do any geometry or calculations with it, as opposed to all other numbers. In our world, we have six races, so we decided to base everything around 6 and its multiples, which includes 12 and 24, including a six-day week.

You could try to go crazy with it and use for example a sexagesimal (base 60) math like the ancient Sumerians did. Maybe your whole story could be in part about the magic of numbers. The only rule to keep in mind is that there is also a reason why mathematical and symbolical systems tend to be based around relatively low numbers. People need to be able to keep up.

The reason why the whole point of numerology is dividing larger wholes into smallest useful numbers is that human mind can process only relatively small numbers of things at a time. People also tend to have small numbers of family members and close friends, which gives small numbers further, deeper meaning. A couple is two people, so that’s what number 2 means — relationship. You can have a love triangle, love square maybe, but not a love myriagon, representative of an affair between 10,000 people.

Although, “Myriagon” would be a pretty cool name for a wizard… Making a note. Anyway, what this means in terms of other practicalities is that a day should have a small number of hours; a week should have a small number of days; a month should have a small number of weeks; and a year should have a small number of months. Otherwise, the calendar won’t be useful to people, and it really needs to be. Based on the range of major arcana in tarot decks, “small number” in numerology means something like 0–24.

The Alchemy of Signs

Finally, once all the bodies in your solar system are tucked in their orbits and once you have decided how many of everything there shall be, you need to look closer at the calendar that you created. Like I already said, it needs to be useful to people. Making it in the right numerical proportions is part of it, but there are additional layers of meaning that ancient people would ascribe to it. A calendar usually was a zodiac, populated with signs, or asterisms (constellations) representing characters and their stories.

The number of (sun) signs should be the same as the number of months, because on one level, signs are the stories about what nature is doing in any given month. This way, the calendar explains to ordinary people what they should be doing in every part of the year, particularly in terms of agriculture. In a magical world, there could be much more than weather going on, so the signs should probably explain the cycle of magic as well.

Beyond that, the underlying assumption of most astrological systems is that people born in a particular season have some character traits in common with the literal nature of that season, resulting in their “fates” being describable in terms of how the seasons evolve over time. This is also connected with the idea of elements, or the basic constituent parts of nature, and by extension of people. The number of elements (ideally a small number) should therefore corespond with the number of seasons.

So, if you have 12 months, you should have 12 signs. Number of elements needs to then be a factor of 12 smaller than 12, so it could be 2, 3, 4, or 6. It shouldn’t be 5, 7, 8, or 9. If you had 16 months and 16 signs, you should have 2, 4, or 8 elements. Generally speaking, an even number of elements makes more sense, or it is at least easier to make it make sense, since elements should holistically cover all of reality. An even number of elements can consist of opposing scales, which doesn’t leave things out.

The classical four elements are fire, water, air, and earth. Fire corresponds with 1 (willpower and individuality), water with 2 (feelings and relationships), air with 3 (change and abstraction), and earth with 4 (stability and structure). The way you get these elements is by combining two oppositions — outward versus inward, and essence against form. Fire is outward essence, water is inward essence, air is outward form, and earth is inward form. You could pick different principles, and make four or more fundamentally different elements, if you’re feeling philosophical.

Notably, there are systems of five elements, like in the Chinese tradition (wood, fire, earth, metal, and water), or in Magic the Gathering (white/plains, blue/islands, black/swamps, red/mountains, and green/forests). The way to work with odd numbers like 5 in numerology is to focus on the aspect of change, or evolution in time. In Chinese astrology, each year is a year of a different element, so the elements are a 5-year cycle. In MtG, the five colors represent what 5 means in numerology — conflict, or strife, permanent instability of 3 sides attacking 2 sides.

MtG in particular is an interesting case to study, perhaps the best thought-out modern numerological system, invented for a fantasy game no less. The color wheel can also be seen as a system of 10 elements, because each color is precisely opposed to a combination of the two “enemy” colors (adjacent colors are allies, not adjacent colors are enemies). For example, white is life/order, while black contains death and red contains chaos.

MtG is also a system of 6 elements, in a way, or perhaps a dual system, as it also has a colorless dimension, which is philosophically opposed to all 5 colors. Thinking about how elements work is basically like doing geometry, only with ideas. If you set and use the numbers right, you may not even need to explain what anything means explicitly, most people will literally draw the same conclusions intuitively, independently of each other.

If you find this kind of discussion arcane, then you’re correct. Coming up with a system of signs and elements that’s fully developed will give a lot to think and talk about to the mages and alchemists inhabiting your world. In the absence of any depth to signs and elements in your world, you will have to resort to clichéd gibberish when writing dialogue or background lore for magic users. Moreover, if your arcane lore makes logical sense, you can then hide a lot of clues within it that math nerds will be able to decipher.

So far, the main uses of astrology that I have personally encountered while playing fantasy RPG games were the character signs in Elder Scrolls games and weeks of something in Heroes of Might and Magic games. These examples point to valid ways of using astrology to inform game mechanics, but are so basic in how they’re realized that they’re almost pointless. Moon gate travel in some Ultima games being tied to moon phases was already way more advanced, and there’s much more fun and meaning to be had.

Let’s look at zodiac creation. The signs in Elder Scrolls games appear to be derived from game mechanics, while it should be the other way around. The main signs are therefore the main playstyles, The Warrior, The Mage, and The Thief, each with three additional signs attached to them (for playstyle variety). There’s also a thirteenth sign, The Serpent, because number 13 is bad, I guess. Well, it is, actually, as a total number of signs in a zodiac, because good luck doing any math things with a prime number.

While I very much enjoy Morrowind, Oblivion, and Skyrim, the astrology component has always felt like a complete afterthought, in an otherwise fairly deep and interesting world and lore. You can’t create a more basic, more limited zodiac. Signs need to have a deeper mythos, more layers, and also a connection to the seasons of the world and the nature of magic.

Choosing a more practical number of them than 13 would be a start, but what’s important to understand is that much like elements, signs should also be a holistic set of archetypes derived from higher principles. In the real western astrology, each sign is a unique combination of one of three qualities and one of four elements. You already know the elements, so the qualities are cardinal (leading), fixed (enduring), and flexible (adapting).

A basic, but very useful way to create a novel zodiac would therefore be to keep this structure, but change the constellations, or the surface symbolism. For example, the sign of scorpio is a fixed water sign, or enduring emotional type, which is why it is described as paranoid, jealous, and vindictive, but also loyal, unyielding, and regenerating. You don’t have to use scorpion-based myths or imagery to communicate any of that.

You could take all of the existing signs and keep their essential definitions, but invent entirely new myths telling stories about their traits. Each sign has a decent range of ideas associated with it, from which you can pick what to focus on and what to downplay. You could also change their order, thus perhaps also altering the progression of seasons on your world.

Such changes are still fairly simple, but could transform the zodiac to a point that barely anyone would be able to tell that it isn’t entirely original. This would also allow you to keep all of the already developed numerical symbolisms used in real-world alchemy or numerology, which you could also tell original stories about using different objects or creatures.

If you’re feeling more ambitious, you could try to create an entirely new type of zodiac with a different geometry based on different numbers and different principles. Ideally useful, small numbers and fundamental, meaningful principles. If you have a solid philosophy of what your story should be about, then making it about that from the basic elements up through signs to the planets could result in something truly epic.

As for what an astrological system should mean for story or game mechanics, you only need to understand that astrology is used primarily for two things — delineations (describing character of something) and forecasts (predicting future conditions). The definitions of signs should therefore describe the nature of seasons, of people, and of the stories you think are important to tell. As for forecasts, Heroes of Might and Magic and Ultima were playing with that a little bit. Basically, it’s all about timing.

In HoMaM, the mechanic was limited to astrologers proclaiming each week to be a week of something. Practically, the only weeks that mattered were weeks of a particular creature (increasing its growth), and the week of the plague (decreasing creature populations). That’s neat, but there’s so much more you can do with this. For starters, more can happen at once.

In astrology, if you have multiple planets that you track, you have therefore at least one time cycle for every time scale. Moon changes sign in a matter of days, rocky planets in the range of weeks to months, and gas giants in the range of years, from a few years in one sign to a couple of decades. This means that there’s a daily, weekly, monthly, yearly, and generational effect.

In this way, it would be much harder for a player to exactly predict the total sum of all effects at any given time in the game, but that’s really more of a feature than a bug. It also means that the effects should be additive, meaning that the same ones add up while opposite ones neutralize each other. This would correspond with planetary conjunctions and oppositions in astrology, but those are not the only “aspects” that you can track.

When planets are at a right angle (at 90 degrees), or in a cross, it’s considered a conflict, and when planets are in a trine (at 120 degrees), it’s considered a harmonious aspect. There are other ones, of course, and in a fantasy world, you can create your own aspects at different angles, anyway. The question is how often do you want some triggers or modifiers of various things that happen in your game in time to kick in. Motion of a planet over an angular distance is much like a hand moving in a clock.

There are so many possible variations of this kind of system that I can’t comprehensively describe them. Have fun with it, go wild. Make it obvious, or make it secret, make it simple, make it byzantine, whatever suits your story or game mechanics. If you use a meaningfully constructed, layered zodiac, I can also guarantee that it will occasionally do something smarter than you intended, or that it will trigger some crazy synchronicity. Not sure why, but complex numerological systems hooked to randomness (like the time when user takes action) tend to generate deep emergent meanings.

For example, when I designed a new zodiac for our fantasy game, focusing only on the numerological theory, and just looked at it when it was finished, I immediately realized that it’s already telling a complete story. That was insane. Not to mention how much time it saved me in development. You can think about it as gamification of the game development process, an area in which I intend to do serious research.

I think that’s enough for now. If you have any questions, I’m pointy ears.