6000 years later a nomadic tribe of mostly humans found one of the secular repositories of magic and technology (mostly technology), called the Diamond Vault by Fourth Civilization archaeologists (the records were kept on engraved slabs of synthetic diamond). These people settled near this Vault and founded a small kingdom. They used the slabs as decoration first, until a half-elf recognized the symbols on them as writing ~1500 years later. She used the knowledge on these slabs to ascend through the ranks and become first the queen dowager, then after her human husband died and her child was still way too young to rule, the queen regent. She passed on the importance of this knowledge to her descendants, establishing a line of scientist monarchs, and the greatest empire of this age. In 1000 years this empire conquered the entirety of the continent and found a second vault, that one offering little in the way of technology but being packed full of magical knowledge.

In the next 1500 years this Empire was transformed into the Ascendancy, an oligarchy ruled by the Ascendants, people who successfully combined magic and technology in ways not nearly approached by the Fourth Civilization or the Giants before, and only seen during the First Civilization. One continent was turned into a nature reserve, and another was left untouched and unexplored for reasons still unknown.

The Ascendant technology made much of the previous technologies obsolete. Mining and agriculture ceased as materials were summoned directly from other planes and transformed into never-before-seen forms. Cities were constructed of a white slightly-translucent stone that was unbreakable when exposed to magic, people were served by magic-powered automatic servitors, information was stored and accessed on black slabs - some of which even capable of speaking and understanding what they are told, and a degree of thinking as well - and some people have even left the planet. The overwhelming majority (99+ percent) of people had magitech implants, improving their mental and physical faculties and arcane capabilities beyond anything that was seen since the First Civilization left this multiverse. They were said to rival the gods in power.

Two features of this age became important later on: On what is now called Golem Island, a technological development facility experimented on fully autonomous and self-replicating servants with minimal supervision. And as the civilization was extremely hungry for magical power, a new type of power source was constructed on the southeastern corner of Boreia that combined automation, power from certain elements in the crust, and arcane transmutation circles to empower the aether.

This led to the final collapse of the civilization. An oopsie in the aetheric reactor released a cloud of magic-infused radioactive particles that drifted over to Golem Island. The Island was evacuated and the reactor was covered in a dome of rock ~2 miles high (known to the Fourth Civilization as the Dome Mountain), but the technological development facility on Golem Island was left running. In the resulting power crisis recovery of that facility was a low priority which was, in retrospect, the worst decision of the Third Civilization.

The cloud altered the base programming of the experimental servitors, making self-replication and self-improvement their #1 priority. In 20 years the island’s resources were nearing exhaustion and the automatons began cannibalizing each other. In 30 years their cognitive improvement reached the point where they realized that this was unsustainable. 35 years after the reactor explosion automaton barges reached the coasts of the nearby continent.

In 75 years the Third Civilization was reduced from a globe-spanning empire of ten billion souls into maybe a million or two people huddled inside shield domes plus another million refugees on other planes protected by the Fae and the Primordials.

Working secretly, some of the Ascendants developed a weapon of last resort, essentially a magitech EMP. When the automatons breached a shield dome that was thought to be completely impenetrable, this remained their only choice. The EMP needed every bit of magical power that the civilization could muster, so refugees were ported back from the other planes too to power it.

Then the weapon was fired.

Every active magitech device on the Material Plane and the Inner Planes fried itself and died, except some that were shielded by an energy shield or miles of rock.

90% of the surviving people died instantly, their bodies being dependent on their implants. They were the lucky ones.

9% of people only had minor brain implants, mostly the standard hippocampus enhancement that took over their long-term memory. They reverted to the level of pre-verbal infants, only remembering a few small details that their organic hippocampus still bothered to store. Some of them even survived for more than a few days. A fraction of these people were children whose organic hippocampus was still active enough to let them live into adulthood.

1% of the people were unimplanted for one reason or another (too young, allergic to the implant, etc…). They spent the remainder of their miserable lives ensuring that sapient life survived. It is them who are to thank for the Fourth Civilization.

An automaton on Golem Island was testing a personal shield in the depths of a bunker. It was a comparatively simple machine, a Constructor, which is why it was chosen as a test subject. If the shield hadn’t worked, it wouldn’t have been a great loss. When the Pulse arrived, it destroyed every other automaton in the room which fell down onto the floor, their artificial mimicry of life cut short. The Pulse penetrated the shield too but was weakened by it, wiping most directives from the Constructor’s mind except the most basic ones hardwired in its brain. It detached the useless shield module from itself, disassembled the deactivated automatons in the room, then slowly and methodically began to build a slightly improved copy of itself. (These eventually evolved into the Golemkin, which are what the Warforged are called in this setting. They are peaceful but isolated by two groups of less-sapient self-replicating ships patrolling the sea surrounding their island, known as the Hungry Sea.)

And this led to the Fourth Civilization. The Ascendants who built this final weapon were in contact with the gods and reached an agreement with them before the weapon was fired. They were made Archons who then descended among the surviving mortals in secret and took samples of their bodies. Then with the help of Fae tree-shepherds and their own knowledge of magic, combined and copied the genes of the people and planted People Trees all over the world. In a few decades, they bore fruit, disgorging functioning adults with no real memory except the skills they needed for survival.

The Gods, Fiends, Fae and Primordials then convened for the first time since the end of the Soul War, and signed the Second Divine Concordat: Communication between Gods and mortals became more open and Gods were allowed to contact mortals unprompted. But there was one important stipulation: No being from outside the Material Plane might reveal information about earlier civilizations that mortals don’t already know. In addition, the Fae and the Primordials were allowed to create new mortal races alongside some other gods who didn’t do so after the Soul War, leading to the birth of the New Fey (e.g. satyrs and centaurs) and other races originating from the Fae and the Shade, the Genies, the Tabaxi, various birdfolk, the Tortles, and the Kobolds.

The New People came to Yphilios with no memory. While the parts of the 1% who survived the Sacrifice and were capable of speech tried to pass on their knowledge, barely any of that remained; it is estimated that only 0.1% of the vocabulary of modern languages originates from the language of the Third Civilization. Some information survived in oral histories, including the fact that the new people were the Fourth Civilization on the planet.

Still, these New People were not any less intelligent than their genetic donors. Witnessing the ruins of the Third Civilization (before they fell into complete disrepair due to not having any more magic keeping them whole) and hearing some strange older people make sounds with a distinct pattern to it spurred them into mimicking these behaviors, attempting to build structures similar to those ruins and using the same kinds of sound patterns to communicate. In addition, the gods themselves shepherded their people, subtly nudging them towards new technologies and revelations. The Fourth Civilization sped through the hunter-gatherer phase in scant 4000 years, establishing their first permanent settlements around 6000 years before Auberentian Reckoning.