The Pillars of Nosgoth are a mystic place of reverence in the Legacy of Kain series of video games. They act as devices through which the land of Nosgoth can be controlled - as the pillars are corrupted, so too is Nosgoth. However, later in the series it is discovered that the pillars serve an alternative purpose: sealing the Hylden in an alternate dimension.
The Pillars are nine white columns arranged in an eight-point semicircle with the ninth pillar in the center of the other eight. The Pillars extend far into the sky and deep into the ground. Each Pillar represents a thing or concept by which the world functions: Mind, Dimension, Conflict, Nature, Energy, Time, States and Death. The center is the Balance Pillar. Each Pillar is served by a sorcerer, selected at birth, who acts as a guardian. For serving the Pillar, the guardian obtains immortality and magical powers related to the Pillar they serve. This group of sorcerers is known as The Circle of Nine.
In Blood Omen: Legacy of Kain, Kain is told by Ariel, the ghost of the Balance Guardian, that the Pillars of Nosgoth govern the land and that as their guardians have gone insane and been corrupted, the Pillars and Nosgoth have followed. Ariel tells Kain that killing the guardians, allowing new pure guardians to be born, will allow the Pillars to be restored, but does not tell Kain that he is her successor to Balance Guardian and thus is one of those who must die to restore the Pillars. Kain refuses to sacrifice himself, dooming Nosgoth to rot until he dies. In the next game, Legacy of Kain: Soul Reaver, Kain has built a fortress around the fallen Pillars, with the Balance Pillar serving as his throne.
In Legacy of Kain: Soul Reaver 2, Kain travels back in time with Raziel, and tells him that the corruption of the Pillars began when the Mind Guardian Nupraptor found his lover, Ariel, murdered, driving him insane and causing the rest of the guardians to follow suit, including Kain who had been born minutes earlier. Although Raziel believes that the Pillars are meant to be guarded by humans, he discovers murals during the course of the game that the Pillars were built and guarded by the first vampires, and were used to seal their enemies in an alternate dimension.
In Legacy of Kain: Defiance, Raziel discovers that the Elder God was the cause of the shift from vampire to human guardians, convincing Moebius the Timestreamer to rebel and place human guardians in place. He also discovers that the vampires built the Pillars to seal the Hylden, their ancient enemies with whom they warred for centuries. Raziel also discovers that the Hylden Lord masterminded the fall of the Pillars by possessing the guardian Mortanius and having him kill Ariel, setting the stage for Nupraptor to drive the guardians mad. As the Pillars have corrupted, the seal on the Hylden has weakened, allowing some of them to cross over into Nosgoth and speed up this corruption in the hopes the seal will break completely. At the conclusion of Defiance, Raziel purifies Kain's sight using the Soul Reaver, healing the corruption Nupraptor's madness had inflicted centuries earlier and possibly allowing Kain a chance to remain alive and still restore the Pillars.