Atlea and Beyond
The Forging of the Living Gate
The Aboleth in ancient times performed a massive horrific ritual that caused the Far Realm (a realm of madness that is inimical to all creation) to bleed into the existence we know, in the Astral Sea. It opened the floodgates and all manner of horrors from that realm found their way here. The mind flayers (or illithid) were created when this happened due to the corrupting influence the realm had on humanoid creatures. To stem the tide of the Far Realm, Ioun, Pelor and Erathis joined forces to help Moradin forge the Living Gate, a colossal crystal that would serve to plug the hole in reality. The Living Gate was not simply a giant crystal, however. It was sentient, a super-organism that had but one desire- to stop the corruption of the Far Realm on reality. The Living Gate held most of the tide at bay, but the Far Realm’s influence could not be completely halted, particularly in places with some affinity to madness (see Forever’s Edge).
Recently, fragments of the Living Gate have been splintering off, becoming Shardminds and falling to various planar dominions.
There are rumours that such an object exists elsewhere as well, in the furthest reaches of the Abyss.