Battle between Tiamat and Bahamut

Religious event

Where their scales landed, they grew into dragons. Where drops of blood fell, the first dragonborn rose. Neither were killed in the fight but both were seriously injured. Tiamat burrowed into the earth, opening the entrance to the Abyss and unleashing the demons. Bahamut coiled his body around the hole, his head falling into the sea, as a barrier against the demons, and it was there that he died.