The cataclysmic destruction of the Valyrian Freehold, the greatest civilisation in the known world. In a single day, the Fourteen Flames (the volcanic mountains of Valyria) erupted simultaneously, shattering the peninsula, boiling the seas, and destroying the Freehold utterly. The cause remains unknown - natural disaster, sorcery gone wrong, or divine punishment are all theories. The Targaryens survived only because Daenys the Dreamer foresaw the Doom and persuaded her family to relocate to Dragonstone twelve years before the catastrophe.