When the Ironworkers - or more accurately the last of them, the title having been an umbrella term equivalent to 'arcanist' in the Imperial Era - attempted to reconstruct reality, they encountered certain difficulties.

As the name would indicate, true iron, the substance upon which humankind's prior civilization had been built, played the foremost role in this process. The ancients had wrought most everything out of iron or some alloy of it since the beginning of the New Kingdoms era, from buildings to accessories to weapons. Even their version of logic engines used it, utilizing a complex system of electromagnetic pulses that was no longer possible in the present day. At some point, it had become understood that sufficiently condensed, sharpened and charged with energy, it would begin to bend the world at strange angles around it, like a heavy object placed on a sheet of suspended cloth.

Even back then, it was already known that the naturally observable universe (or the birth plane of human beings, as it was conceptualized in the present) was, in truth, only one intersection of 4 discreet dimensions in a true world that contained at least 11; a single perspective on a grander reality that was vastly more complex then could be conceived of. What were once thought of as elementary particles were in reality just one face of a many-sided die, and what looked like a tree, or a mountain, or a star to us, could in another plane be...

Well, something impossible to even conceptualize. A piece of an otherworld where things worked so differently on an essential level that trying to visualize it would be as alien as a stick figure trying to understand the concept of 'sideways'.

I'm getting off-topic. My point is that iron, in that special state, was found to physically transcend, or at least influence, dimensions beyond the four native to humanity, warping other planes, which then warped our own in turn. In the following centuries, this evolved into a very exact science, enabling things that had once been thought impossible, like travel between the stars, or even their own efforts towards immortality and the transformation of the human condition, now half-lost as a byproduct of divided and secretive sects of scholars.

At the time the collapse arrived, scholarly understanding of the cosmos, though comprehensive, was still far from complete, and even this power had no hope of stopping it outright. It was, however, advanced enough to allow the creation of an cross-planar edifice of iron that was not dependent on 4-dimensional reality, and which it could not reach. There, what human beings had the luxury to be sufficiently prepared could continue to exist (after a fashion), and the edifice could be expanded to construct new planes in which they might eventually live.

There's a term which comes up in many forms of scholarship: 'Substrate'. It essentially means the foundation of something which also, to some extent, defines its format and nature. For example, a canvas is the substrate for a painting, and a brain is a substrate for the human mind.

A substrate cannot exist within itself. That sounds awkward when I put it so directly, but it's not too hard to understand if you think about it in abstract-- A foundation obviously can't support another foundation of equal weight and nature, because... Well, it would make nonsense of the whole premise. A book is a device for storing information, but it cannot contain within its letters everything about itself and what it contains, because that is already more than it contains. A box cannot hold another box of equal size, unless it is bent or otherwise changed. A mind cannot hold another mind...

Iron, or more specifically that edifice, the Tower of Asphodel, became the substrate for the mortal planes. Which meant that true iron could not exist within it.

Broadly speaking, this wasn't the end of the world. As a mundane element, iron can be replaced in most of its roles in geology and nature by copper, titanium, and various alloys or artificed elements, and the Ironworkers eventually discovered how to hide its absence altogether at a cosmetic level. But biologically, human beings also contain iron, and one of the paramount goals in the reconstruction was to preserve what it was to be and feel human for those who had 'survived'. It probably wasn't until those days that people really understood how delicate a thing that really is. The strange balance of chemistry, electromagnetic crackling, and sensory pulses that, when you're alive, feels so absolute...

A few less-than-logical beliefs around the topic played a role, too. With all the impact that iron had on human civilization, some, even among the Ironworkers, had begun to see it as almost an inseparable aspect of human existence, like it was a part of the soul. I suppose it goes to show that nobody is completely immune to superstition and magical thinking.

But, in any case. The result of this was that the human body was rendered a sort of impossible object; something that could not exist by the very laws of reality itself.

At least, not conventionally.

Some human bodies, or at least the impression of them and the iron within, had been preserved as part of the Tower, frozen in a timeless place. And because of that, it was eventually discovered it was possible for them to exist in the artificed planes as a sort of stable paradox. After all, while a book can't exist within itself, it can still reference other stuff it does contain internally, even if it makes for somewhat awkward reading. A few tweaks and workarounds solved the problem of the iron associated with that human body staying a part of it, and just like that, human beings were walking something at least akin to the earth once again.

However, this only permitted replicas of those bodies within the Tower to exist. The creation of new ones remained impossible, and births not incubated by anima taken by the same mechanism would inevitably fail. And there were far fewer preserved bodies than minds; scarcely more than ten thousand or so for each party.

And though multiple copies of the same body were able to exist at the same time by utilizing this method, it was an existence that was fundamentally unstable. If you have a single egg, and reach through time to grab it from a day in the future, you do not now have two eggs, but rather the same egg twice. And should you try to mix the two together into an omelette...

Well.

There were... Some disagreements that had happened, after that.

It wasn't so bad, most of the time. If everyone could afford high-quality distinction treatment, it wouldn't even be a problem at all except for touching, and that could be easily avoided just by keeping covered and making sure your numbers didn't overlap. Even as it was, you could forget about it most of the time, other than the occasional disaster like this.

Thinking about it directly was, of course, really, really unsettling. Another reminder that the Ironworkers hadn't made things quite as they ought to be, but had merely established a convincing simulacrum. But it was convincing, at least, so if it were the only way in which they'd struggled, it would be okay.

But if you've ever been part of any sort of technical project, one thing I'm sure you'll understand is that sidestepping one problem tends to create, or exacerbate, another.