- "The Pillars choose their guardians from birth, Raziel – and vampires are no longer born.
This is the crux of our dilemma.
And this is the terrible irony – with their vampire purge, the members of the Circle have assaulted the very architects of the Pillars they are sworn to protect.
They have embarked on a treacherous path. With every vampire they kill, the humans are slitting their own throats."
- ―Janos Audron — Listen (file info)[src]
In the Legacy of Kain series, The Pillar Guardians also known as the Circle of Nine are the order of sorcerers whose duty it is to guard the Pillars of Nosgoth, a Tenth Guardian existed; Janos Audron who wasn't tasked with serving a pillar but rather the key that would restore the pillars, the Soul Reaver.
The Circle of Nine were a group of individuals, chosen from birth to wield the powers of the Pillars of Nosgoth. Each Pillar had a single 'Guardian', and that person was symbiotically bound to it, as the living embodiment of the force it represented. That individual was also bound to the other eight Guardians. Together, the Circle functioned as a single entity, with the Balance Guardian as "the hub, the still point around which all the other Pillars principles turn". It seems the role of the Balance Guardian was to regulate the energies of the Pillars to keep Nosgoth stable and healthy.
When the Pillars were raised, the original nine Guardians along with the tenth secret Guardian were Vampires. Since vampires could no longer reproduce, a result of the Hylden curse, they would turn any new Human guardians that were called to serve into vampires. This tradition continued until Moebius and Mortanius, who had been called to serve as Guardians of Time and Death, revolted against them and claimed the Pillars for humankind.