Doom of Valyria

The Doom of Valyria was the cataclysm that destroyed the Valyrian Freehold, the greatest empire the world had ever known, in a single day roughly a century before Aegon's Conquest. It shattered the Valyrian peninsula, ended the age of the dragonlords, and reshaped the history of both Essos and Westeros.

The Cataclysm

On the day of the Doom, the Fourteen Flames, the chain of volcanoes that ringed the Valyrian peninsula, all erupted at once in a convulsion of fire and ruin. The land was torn apart, the great city of Valyria swallowed, and the dragonlords and their dragons destroyed. Where the peninsula had stood there remained only a scatter of smoking islands and a poisoned, fog-shrouded sea, the Smoking Sea, ever after shunned by sailors.

Causes

The true cause of the Doom is unknown, and the maesters and scholars offer many theories: the natural convulsion of the volcanoes, the failure of the spells the Valyrians used to bind the Fourteen Flames, or a divine judgment upon their pride and cruelty. Whatever its origin, it came without warning and ended five thousand years of Valyrian dominion in an instant.

Consequences

House Targaryen, having abandoned Valyria for the island of Dragonstone twelve years before the Doom on the strength of a prophetic dream, survived as the last of the dragonlords, preserving dragons that would one day conquer Westeros. The Free Cities descended into the Century of Blood, warring over the ruins of the empire. The secret of Valyrian steel and much ancient lore was lost forever, and the Doom remains the great rupture between the ancient world and the present age.