Domain Of Dragons
In the days before Tiamat and Bahamut came into their power, no dragon ever died. Beasts and men passed from the world, returned to Io, and were reborn; but dragons were immortal. When Io was lost, things changed.
The mortality of her dragon children disturbed Tiamat. She had stored within their minds great portions of her knowledge, which was now lost. That lost learning was a galling blow. Tiamat came to hate death, which she saw as the enemy of comprehension.
Tiamat directed the force of her knowledge to the task of ending death. For many years the sentient creatures devoted to her researched the undoing of death. It is through these experiments that undead came into the world. When it became clear that undead could not be created without doing harm to the soul of the creature, Tiamat commanded that the endeavor be abandoned.
Instead, Tiamat discovered a way to channel the souls of the deceased into her own realm. There she records the stories of their lives in her grand library before sending them on to be reborn. Unfortunately, Tiamat is unable to use this solution to preserve the knowledge of dragons because their souls do not travel in the same way that Io’s creations do. Tiamat still searches for a safe way to preserve the thoughts of her progeny.