The event that ended the Meridian Age and began the current era has no agreed-upon name, which is itself significant. Every civilization names its catastrophes. The unnamed catastrophe is either too recent to have achieved mythological distance or too foundational to have been experienced as an event from the outside — it was not something that happened to the world, it was something the world became, and you cannot name a becoming with the same grammar you use to name a happening. The closest thing to a common term across current cultures is simply the Descent, used with the lowercase casualness of a word that has been in circulation long enough to lose its capital letters, like saying the dark rather than the Dark Age — as if the darkness is too ambient to require formal designation.
Three hundred years ago, approximately — the records are inconsistent in their dating because the calendrical systems of the Meridian Age collapsed along with everything else and were reconstructed imperfectly by their successors — something changed in the Lattice. Not dramatically. Not with the violence of a geological event or the spectacle of a supernatural one. The change announced itself in the way that the sinking sun announced itself: through accumulation, through the slow failure of things that had always worked to go on working. Crops grown in soil that had been productive for centuries began producing yields with a subtle wrongness to them — not poisonous, not obviously diseased, but nutritionally hollow in ways that took a generation to manifest as the softening of bones and the dimming of cognition in populations that had eaten adequately by every prior measure. Navigational instruments began producing readings that disagreed with one another by margins too small to matter on any single voyage and too consistent to ignore across a decade of voyages. Architects working in the traditions of the Vel Sorath found that measurements they had taken accurately in the morning did not match measurements taken of the same surfaces in the afternoon, and that the discrepancy could not be attributed to thermal expansion and could not be reproduced on demand and could not be explained by anything in their technical literature.
None of this, individually, would have been sufficient to end a civilization. Civilizations endure crop failures and instrument drift and architectural anomaly. What ended the Meridian Age was not any single failure but the realization — slow, distributed, uncoordinated, arriving in different places at different times and through different means — that the failures were not failures. They were communications. The world was not breaking down. It was changing its behavior in response to something, the way an animal changes its behavior in response to a presence it has detected before you have. The people of the late Meridian Age did not know what the world was responding to. The people of the current age are not much closer to knowing. What they know, or what the most honest among them admit to knowing, is that whatever moved in the Lattice three hundred years ago has not stopped moving, that its motion is not random, and that the direction it is moving is toward the surface.