Several hundred years ago Tiamat, the goddess of greed, wealth and vengeance lead her army of dragons against the world in an apocalyptic war, cities and kingdoms fell and the world was almost brought to ruin before Bahamut and Moradin stepped in. The dragon king and the creator fought alongside the heroes of old and defeated Tiamat and her army. Bahamut felt ashamed that his race would forever be disgraced by Tiamat but he had to act for the better of the world.
Once they had contained the immediate threat Moradin pulled the magma and rock from the core of Ekoth to form an island in the middle of The Great Sea. On this island they built a tomb and sealed Tiamat inside, chained to the very core of the earth. The tomb became known as the Tomb Of The Nine Hells due to the high demonic activity that went on in and around it. The island itself was sealed in a magical barrier that prevented flight within it and greatly reduced the magical power of any within.
Brimstone Isle as it is known is a prison for all dragon kind, except a few clans of Dragonborn dedicated to Bahamut who were set free but watched carefully by the gods. Due to this Dragons are a rare sight and are associated with the end times. Dragonborn are now feared but are still respected since it is assumed they are devout worshipers of Bahamut.
The island, when viewed from the outside is shrouded in a veil of fire that masks its size and the dragons within. Ships that stray to close often find the waves themselves pushing them away from the island as though the island was physically repelling them