The Genesis of the Pillars

Banishment means nothing if it is not enforced. The Ancients knew this and so they forged nine massive pillars from pure magical energy. They then mystically bound these great pillars into the very life of the land, each Pillar magically and inextricably connected to an integral element of the very fabric of the world so that their magic would never fade. As long as the pillars stood, the boundaries between realms would be locked into place, leaving the Hylden with no means of returning to Nosgoth.