"She began hunting the fae swarms then,"  Swarm said. "And I doubt I would have been an exception. So, of course, I took steps. I made myself a cozy little shelter far, far away. I inscribed it with every protective rune known, and powered it using the life force of the very life outside the cave. It was a perfect defense. Nopony could come close to it without their very lives being sapped to further protect me. I don't think Celestia herself could have broken me out of that cave. Not without knowing how to disable the shield at the entrance." 