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From A Wiki of Ice and Fire
Location on the Essos
The Valyrian Peninsula is a large land extending south from Essos into the Summer Sea. It was the heartland of the Valyrian Freehold and the location of the city of Valyria. The Fourteen Flames extend across the neck of the peninsula.
The peninsula was partially destroyed in the Doom four hundred years ago. Many islands were formed and low-lying areas were flooded, creating the Smoking Sea: