The Veil

At the conclusion of the Dawn War, the Twelve needed a way to bind the Corrupted Gods so that they could never cause such havoc on the Material Plane again. After much consideration, they decided to create the Veil, a barrier between the Inner and Outer Planes. This barrier would prevent them from entering the Inner Planes just as much as the Corrupted, but they felt that this was for the best; both sides had contributed to the destruction and drawn countless mortals into their causes. If they all left, mortals would be free to live their own lives.
The Veil is anchored in place by sixteen Keystones: great crystals embedded in the top of each portal in the Outlands. These stones prevent the gods from leaving their realms, but do not prevent other entities such as fiends or celestials from getting in or out; mortals, however, need to meet specific conditions. They Keystones are effectively indestructible, just like the gates they're attached to. No one has devised a way to destroy them over centuries of trying. (Those who do manage to strike a Keystone discover that they emit an incredible blast of pure force when struck, which completely pulverizes the poor fool who did it and anything else in a 60ft radius.) If someone were to hypothetically figure out how to destroy a Keystone, it would blast the portal wide open, allowing even the gods of that realm to travel where they please. Hopefully, that will never happen, because nearly all of the people who would bring down the Veil are worshippers of the Corrupted Gods.
Despite this, the Veil is not totally inpenetrable to the gods. They can still reach through it with some of their power to send information and bestow boons on their worshipers.

Type

Metaphysical, Supernatural