They were first created by Tiamat in order to wage war against the younger gods for the murder of her mate Apsu. In the Epic of Gilgamesh, they stand guard outside the gates of the sun god Shamash at the mountains of Mashu.
These entities were made by Tiamat to combat the younger gods for the murder of her mate Apsu, and they guard the gates of Shamash at the mountains of Mashu.