Transitive Planes
I, like many game masters, love the process of world-building.

Creating new settings whether with new rules or twists on classic fantasy paradigms is extremely fun. They can be created whole-cloth, with a guide, by smashing together themes and concepts from popular media or any number of other methods really. Creating an environment for adventure and for adventurers to explore is just incredibly rewarding.

And it can also be as involved and time consuming as a GM wants.

It’s an exercise I’ve engaged in many times and one that I know I will continue to.

In fact, I have plans to do so for a number of different systems that I am particularly interested in running and would love to build some worlds and settings for.

But I also love what I like to refer to as “Transitive Settings.” They are a kind of meta-setting that can be a location for adventure all it’s own, or can connect to existing settings to facilitate even grander stories. Although many games and systems have such environments, in Dungeons and Dragons we have a couple of classic examples to look at.

Planescape
Maybe the most famous (and most recent for official WotC 5E) would be the Planescape setting. Originally released for 2E D&D and then updated for 5E in 2023, this setting creates a sprawling world of connection between the different “higher planes” that existed in D&D lore almost since its inception. Planescape also acts as a mechanism of sorts for traveling between planes, both the 16 high-minded philosophical planes detailed in the setting, but also the different worlds of the material plane.

It also introduced the Outlands, a sort of planar milieu where the themes and concepta of the 16 outer planes start to smash into one another physically.

And then conveniently situated at the center of the Outlands is a cosmopolitan bastion of civilization, a city only accessible via direct portal and teleportation.

I’m talking about Sigil of course.

Sigil symbolizes the idea of a “Transitive Setting” incredibly well. The magical modalities of travel required just to access the city instill the concepts required for interplanar (and inter-world) travel. The diverse make-up of its citizenry, and the bizarre almost alien ruler who oversees the place (the mysterious Lady of Pain) quickly brings into focus that other worlds beyond the characters own exist. And they can be accessed from right here within this city, as long as you know how to do so.

The Radiant Citadel
Planescape is not D&D’s only “Transitive Setting”, though.

In the true definition of a “Transitive Plane”, the Ethereal plane is one of, if not, the oldest example of a “transitive plane” in the game, it just never had much else to explore within misty depths.

The Ethereal Plane is a sort of ghost realm or shadowy, hazy projection of the real world that exists right next to it. It is a place that people in the material plane are not acutely aware of existing, but instead catch glimpses of from time-to-time, often out of the corner of their eye.

Unless of course they have True Sight and can see straight into it.

Now, within the 5E Era of D&D, we received a brand new plane or dimension-hopping vehicle in the form of the Radiant Citadel.

Tucked away within the Deep Ethereal, the Citadel connects to as many as 27 different worlds.

So, again, the ability to connect disparate worlds (both the fifteen detailed in the book itself and the twelve undiscovered worlds that also connect) is perhaps the second “Transitive Setting” that we have received in recent years.

Spelljammer
We also had a return to the Spelljammer setting, also originally from 2E, within the 5E era. Spelljammer creates a space-fantasy type of setting for Dungeons & Dragons.

It also creates a sort of physical way for PCs to travel from world to world by boarding these magical ships (Spelljammers) and sailing them across the stars. This is in stark contrast to all the “portal” based travel methods observed in some of the other settings. (And yes, I know about the Concord Jewels from Radiant Citadel, but they just go point-to-point, so it’s not quite the same thing.)

In Spelljammer, every major setting that could be said to reside on the Material Plane is sort of envisioned ultimately as a planet in it’s own solar system (called a Wildspace System). If you possess a Spell jammer you can bodily fly from Faerun, to Oerth, to Krynn, and back if you wanted to.

The Great Wheel
Before all of the previously mentioned settings was something called the Great Wheel Cosmology, which things like Planescape, Spelljammer and even the Radiant Citadel have attached to and expanded on slightly. The Great Wheel is ultimately an ordering of the Material Plane, the Inner or Elemental Planes, the Outer (or philosophical) Planes and the Positive and Negative Energy Planes. Not really a “Transitive Setting” in it’s own right, but certainly a valid mention since it gives a kind of “global” shape to the planar cosmology of the game. This cosmology was also tweaked and twisted and made a slight variant of in 4E D&D as well.

Planebreaker
Other third-party D&D creators and other game systems have also created different methods to connect the different settings and worlds of our fantasy role-playing games together.

A great example would be Monte Cook’s Planebreaker. Essentially, Planebreaker is a giant comet that can travel between planes. It sort of punches a hole into the reality of whatever plane it travels to, bringing with it both weird, unexpected creatures and magical effects that might start to change a world. It then will take (or accidentally transport) some of whatever makes up the world it’s currently in with it, whenever it deigns to leave for the next world.

People can get linked to this energy and can travel back through the worlds that the Planebreaker comet has punched into.

But where it goes and how it is manipulated to move from one plane to another is not common knowledge in the way that interplanar travel might be common knowledge in some other settings.

The Labyrinth
Another noteworthy “Transitive Setting” is Kobold Press’s recent Labyrinth setting. The Labyrinth creates an amorphous network of portals, shadow roads, leylines, cat slides, tunnels and other transportation metaphors to move creatures around their cosmos.

The Labyrinth presents a fun alternative to something like D&D’s Great Wheel, with its own unique history and structure. It features an asymmetry to its layout (even if that actual layout is just a conceptual framework) that is really interesting and engaging and it feels noticeably different from the Great Wheel.

Underlying the whole setting is the fight of all sentient beings (good and evil, but mostly good) against the nihilistic Void and its factions. Adventurers in the Labyrinth almost always are affected by the undercurrent of this perpetual battle for existence itself.

But why though?
So why am I giving you this sort of history of other “Transitive Settings” or planes and how they can connect? Well, the short answer is because I’m working on my own, and we can learn a lot by studying others.

What we’ll see in the next couple of articles is what I’m calling the Archivum Ragnorum or the Archive of Realms.

The Archive of Realms sits tucked away in a pocket of space where sits a structure that some may consider as old as the multiverse itself, or almost as old.

The Archive is a library that persists outside of space and time.

Its sole purpose is to catalog the untold number of worlds and realms that exist across all the far-flung corners of the multiverse.

Within its ancient walls, a species of monastic librarians known as the Keepers of the Realms, use their magical observatory, the Planetarium Infanitum, to find new worlds across the cosmos.

The Keepers record their observations of these worlds and keep these records within their archives.

Their records are not merely descriptions and accounts of the worlds however, but the books, tomes, scrolls themselves that the Keepers pen, are in fact portals to each of these surveyed worlds.

Each portal requires a key, which may not always be a physical object, and in fact, in most cases is a specific phrase or passage to be read from the text itself, though that is not always the case.

If this sounds a little bit like the game “Mist” or “Riven,” to you…well you’re right. They played a big part in conceiving of this form of planar connectivity.

I think this concept of an interdimensional library of worlds, of portal books that can transport you to different places, is a really fun concept, and one that I haven’t really seen used before in the TTRPG space (insert comments telling me about a product I never heard of that does this lol). I fully intend to expand my use of the Archive further in my own home games as a mechanism of travel amongst the different planes.

We oftentimes conceive of these worlds, and different fantasy role-playing games in general, of having different themes or different distinctions. These differences can be clear if you compare something like the high fantasy of the Forgotten Realms with the grimdark fantasy of Etharis (from Ghostfire Gaming), or even the grittier, old-school fantasy of Shadowdark and its forthcoming Western Reaches setting.

There’s different tones that we can have in our games and as such, the Archive will not be tied to any one specific rule set.

Instead, the Archive and what we develop for it in this blog going forward, will be setting and system neutral content. This way you can use the Archive with whatever system you’re playing in.

In fact, the Archive as a setting permits a Game Master an opportunity to change systems mid-campaign, or to create a framework for a group wanting to try out different systems. Imagine a campaign built around adventurers who dive into the worlds via different books, taking on different roles in each of these different worlds, and being bound by the “rules” that govern them.

These are just some first thoughts.

Future articles, as mentioned, will expand on the Archive and how it operates. I’ll explain more about the mysterious Keepers, and by what process they’re able to create these World Books, and so on.

So next week we’ll start looking at some of the finer details of the Archive, what makes it tick, and start thinking about how we can use it in games at our tables today.

See you next time.

– Mike