It is said that when the seven pillars were formed and felled, seven pillars of an equal and opposite force were created. It was believed that when these original pillars of virtue were replaced with the representing Elements of Harmony, the opposing force was lost. Though it is true that the pillars of darkness were lost, it was not because of the elements or the original pillars of virtue.
The following is a tale that has been transcribed and translated to the best of the abilities of two generations. A long, long time ago, it is said that Equestria fell into ruin long before Discord had his way. The new world that we knew was struggling to be born as it attempted to cut itself free from its old chains.
Embodiments of the sun and moon had begun on a hunt for all life, thirsting for the blood of everything. Shadows, ponies, griffons, any creature that had ever felt safety in the shadows, any creature that ever felt safety in the light of day. Burned. Slashed. The beings born under the light of day ran from a terrifying alicornmonster born of the moon, and the beings born from the shadows were hunted by a demon of sunlight.
The followers of the shadows, powerless against overwhelming force, fought back with all they had united under the banner of a Mother Sister Queen of Shadows, eager to protect correct avenge the death of her Prince of Shadows. But it was not enough, and their brave forces were driven back.
During the chaos of the world, plunged into an era of fear and disharmony by the loss of the Prince Of Shadows, seven beings pillars awoke from their slumber. They saw the destruction in the world, and wept openly for every life extinguished on both sides and in the memory of their lost master. These pillars did not seek revenge like the Queen, nor did they choose to fall to the broken friends monsters that their master had once called friends. Instead, they wept fierce tears which cut and shaped a hole into the earth, divided in a layer for every heavenly shadow that wept.
Acting in the memory of the prince, they formed these layers to be capable of protecting the lives within from all harm from the outside, and called upon the subjects of the shadows and its followers to search for this bastion of safety. The Queen, needing soldiers and followers, called her loyal subjects to her, and formed a great rift between the followers of the Prince and the followers of the Queen.
In order of descension, the safest and deepest layer was created by and in the name of Peace. The second layer, mercy, the third layer was compassion, the fourth layer was justice, the fifth layer was perseverance, the sixth layer was love, and the seventh and last layer was known as loyalty. There was also another theorized layer, known as the layer of dreams. These layers, were parodies, or imitations, of the virtues.
It is stated that when the seventh pillar sang the last song to lead their weary subjects homeward, the time for salvation was done, and as the monsters descended upon them, they sealed themselves away and vanished, sending the princes subjects to safety and leaving the monsters to squabble over the world by themselves.
We know not its exact location, nor the name, nor when it will return, only speculation. Perhaps it will never return, perhaps it will return when a new prince is found, or perhaps it never existed.
Time will tell.