The first civilization to grace the surface of the Dream World just happens to be the Luminae.
The Luminae Epoch marks the dawn of the Dream Realm, an era where ethereal beings known as Luminae established the first civilization.
Not only did the Luminae's constructed the Luminous Cathedral, it seems they are also the one that created this library.
Probably to store repositories of dream lore and some arcane knowledge.
So their fall is due to the fact that they attempted to delve too deep into the fabric of dreams.
It's just like the words on the stele had warned.
As a result of them delving too deep into the enigmatic fabrics of dreams.
It resulted in the unleashing of a powerful chaotic energy that tore their cities apart.
Probably leading to the destruction of that entire civilization or probably just most of them."
Zeras came to this conclusion after pondering on it.