The Lost Epoch of Khaldun

One of the original building blocks of Crux of Eternity was the existence of convergences — places where other dimensions leak into the world. (They're always written in bold. I don't know why; it just feels right. A tip for new GMs: not everything you do needs to have a reason.) Although this was a cool, mysterious detail, the real reason for this is to provide a plausible framework for including other people's content without stretching credulity. Your FLAILSNAILS character comes to Khaldun and finds another Tomb of Horrors? Blame convergences. The fungi from Yuggoth show up, even though they're really not from around here? Again, probably convergences.

I can introduce all sorts of hot nonsense, and when the PCs ask why winged cyber-boars are attacking, I just throw my hands in the air and say, "That's convergences, babey!"

(Convergences have steadily been getting worse and more numerous over the past couple of centuries, but that has an easy explanation: Morana the Forsaken has been tearing open convergences, hoping to open the right doorway that will resurrect her dead family while remaining utterly heedless of the cost. Now that she has been destroyed, that problem will probably get better. With the possible complication that a complete list of convergences exists in the Archive Adrift's Codex Canalium... which has already been seen by mortal eyes at least once before to scribe the Book of Salientian Hours for the Bogbeast Fens' Temple of the Frog. Among other blasphemies, it's how the cultists knew where to find The Egg.)

Well, a year or two ago, a player learned about the convergences and the fact that they were getting worse, and idly wondered why that might be. The campaign ended before it became important, but it occurred to me that I didn't know why they existed in the first place. (Once again, kids: world-building is fun, but only useful inasmuch as it gets used at the table or informs your decision-making. If it doesn't need an explanation, don't feel the need to give it one.) The immediate answer my brain conjured was some vaguely-considered idea that reality was damaged when the gods and primordials were fighting, and that damage is still ongoing. It didn't feel 100% satisfying, but if someone dropped a legend lore right then and there, it's something for me to riff on and develop further.

Ultimately, no one asked, and so I neglected the question, instead focusing on other activities.

However, I was recently inspired by a detail introduced into D&D lore by Fizban's Treasury of Dragons. They introduce dragons as consummate creatures of the Material Plane, so much so that they (and things tied to them) tend to recur across various alternate Material Planes in the multiverse. So, there might be a version of Benthosruthsa from Castle Whiterock on dozens of Prime Material Plane worlds — an easy excuse as to why several different GMs have run that adventure in their home campaigns and yet all those campaigns represent different fantasy worlds if taken holistically. (In terms of "things tied to dragons," the book gives the example of the many manifestations of the Tomb of Horrors occurring because Acererak killed a lot of dragons to help make it.) Some especially potent dragons even have dragonsight, allowing them to communicate with these extraplanar manifestations. Those dragons might engage in plans that span multiple worlds simultaneously.

To tie this all together, they introduce a new mythology of "the First World," wherein the dragon gods made one world, something happened to sunder it, and that made the sprawling multiverse in which all fantasy games take place.

(I stick with a Planescape-esque "all myths are true" vibe in my fantasy games, so even though the First World isn't necessarily the truth, it is still potentially true, you dig?)

That spiraled in my head to form a rationale for the convergences: a lost epoch of Khaldun, wherein a potent and despotic draconic emperor attempted to reunite the worlds in a grand ritual. (While this would have greatly amplified said dragon emperor's power, it would have destroyed the cosmos as we know it, collapsing all potentials down to just one.) The ritual failed, but the convergences remain as residual echoes of the attempt, linking various dimensions on a fundamental level. Since the gods weren't especially keen on having anyone attempt to reunite (and destroy) the multiverse again, all records of the world-spanning empire were destroyed, and it now exists only as a series of curious anomalies in the historical record. (And perhaps the occasional artifact for a delving adventurer to find.)

Of course, that assumes we can truly be sure that a nearly-godlike dragon emperor with potent sorceries and a consciousness spanning whole worlds is truly dead and not merely sleeping...