I've looked into C'tis a bit, and other than one of their priest units having a greek origin, I can't trace them to any historical civilization.
They could represent some mythological race like Jotunheim, or they're possibly a mix of cultures.
Or its possible not every realm presented has a real world parallel.
Although it'd be odd for all but one to seemingly have one. But R'yleh is based on a book I guess, so maybe something similiar could be for C'Tis.
