The Desolation is the name that has been assigned to the a disastrous event that occurred on Thémos during what scholars now call the Age of Shadows. No one alive remembers what happened to cause such destruction and death. Some say that a star fell from the sky, causing mass casualties and throwing the world into a dark age. Others add that the star itself unleashed a hoard of monsters on the world, and is the origin of all nasty creatures. Many believe these tales to be myth.
The truth behind this massive loss of population and knowledge is a mystery.