Great Calamity

The event that predates, the Godsfall desert and immediately precedes the dark ages where much lore and understanding was lost do to mass societal collapse. No one is sure of the actual event that took place only speculations toward there being a verdant land within the Godsfall desert just prior to it.  If you believe the tales within the Pantheon of the Nine it is stated that Erastil had some influence on sheltering Greensward from this Calamity noting it would likely be a singular event.