So, There two large watch towers on either side of Ishgard: the Stone Vigil (the dungeon), and the Steel Vigil (the place where Svara spawns). I get the Stone Vigil lore -- it fell after the chaos of the post-Calamity. What I can't find is the lore behind the gutted Steel Vigil.

When did the Steel Vigil fall? Was it to the Dravians or something else? What was its principle function?