The Cosheus Abyssal marks the great “world wound” where the horde of demons was cast down in The Sundering/Bale Times.
It is known that The Clearvor (Desert Giants) built the Southgate Span bridge over the Chasmlands at Southgate Garrison.
This refers to the unique environment and cultures/dwellers that have come to live inside and at the bottom of the Cosheus Abyssal.