|“||Cry, Brethren, for the Betrayer is Come. Your Hands will be Crippled, and you will Perish as the Wretched Outcast in the Bleak Unwritten. And you will know the face of the Destroyer.||”|
|— The Prophecitus|
The First Dark Age was described as a time when the Trickster would return and tip the balance of the civilization back towards savagery as charted in Thief: The Dark Project.
The Second was when the Hammer faction stood in full force behind a mad prophet, Karras and shifted balance again. This was charted in Thief II: The Metal Age.
The third had the keeper faction itself lose balance and ended up with the Glyph's destruction as charted in Thief: Deadly Shadows