1. Timeline: History of Westeros
(World of Westeros/History)

...  500 - Targaryens leave Valyria, land on Dragonstone 400 - Doom of Valyria - Dothraki ride out of the east 400 — 300 - The Bleeding Years 300 AGE OF THE DRAGONS - Harren ...

2. The Age of Dragons
(World of Westeros/History)

... time that some great cataclysm befell it, known to all hereafter as the Doom of Valyria, shattering it with fire and ash. What had taken millennia to build was destroyed in a day. This catastrophic event ...