The Fourteen Flames is an immense chain of volcanoes extending across the neck of the Valyrian peninsula.
The Valyrians sheep-herding folk of the Valyrian peninsula, discovered dragons lairing in the Fourteen Flames, leading to their rise to power. Later the Valyrians sent their slaves to mines in the Fourteen Flames, searching for gold among other things. Sometimes firewyrms were encountered in the shafts of the mines by the slaves, leaving only corpses.
“Fourteen or fourteen thousand. What man dares count them? It is not wise for mortals to look too deeply at those fires, my friend. Those are the fires of god’s own wrath, and no human flame can match them. We are small creatures, men.”