It is known to all Fae that the Cornerstone is what holds Aradeyl together. Without it, Aradeyl would collapse into nothingness. It is the most powerful magical artifact in Aradeyl, and while it still existed, it was heavily guarded. No one could go near it without the right permission, and every person who approached was searched, checked, and closely monitored by the The Knights Primeval , an organisation solely dedicated to protecting the Cornerstone. And yet in spite of all that, one day, someone got close enough to the Cornerstone and shattered it...
The intact Cornerstone was a towering monolith of jagged crystal, like an oversized piece of quartz suspended in mid-air of its own magical properties. During the day, it appears as a sheer, purple-blue piece of crystal, occasionally pulsing white and blue, and rotates on an axis, following a pattern known to itself. During the night, the glow becomes brighter, and some observers have testified to seeing twisting wisp-like mist swirling in the crystal. A few have sworn that they saw screaming faces, but those observations were dismissed as a product of an overactive imagination.
The Cornerstone was named for its properties - that is, the cornerstone of the Aradeyl plane. It was believed to be the source of all magic and life on Aradeyl, holding the plane together and ensuring it could exist. It also served as an indicator of the plane's safety and stability - if it were to flash red, or weaken, the consequences would be catastrophic for the plane's inhabitants.
It was also rumoured to be host to the Beacon, who would appear in times of trouble to give guidance or to warn of danger. It is unknown as to who had ever seen or heard of this spirit, but with the Cornerstone broken, it is unlikely anyone would hear from the Beacon again - if there ever was one to begin with.
Recorded history states that the Cornerstone was first discovered by the original settlers in Aradeyl when they fled to the plane. However, the settlers were hotly pursued by humans, who were hell-bent on eradicating what was left of the Fae. When the humans discovered the Cornerstone, they were desperate to get their hands on it and to bring it back to their world, where they could use it for their own purposes. In the battle, the Cornerstone began to wane in power, causing Aradeyl to grow even more fragile.
In desperation, the Fae gathered to put forward a plan to protect their newfound sanctuary. It was in this meeting that the Offering was borne: all Primeval Races save one would sacrifice themselves to power the Cornerstone, and expel the humans from Aradeyl for once and for all.
However, when the time came, one of the Primeval Races, betrayed the others, causing the Cornerstone to be re-powered, but not to the full extent it had been before the humans arrived. This race was known as the Fallen, and as punishment, were damned to be hunted across Aradeyl, until they were all exterminated for their part in the betrayal.
After that, the Fae enjoyed centuries of peace and quiet in Aradeyl, growing and living in harmony on the plane. There would be occasional conflicts between settlements, but none of the persecution they had suffered at the hands of the humans.
There were also times when the Cornerstone would wane and weaken, causing catastrophic storms to rage across Aradeyl, or for the crops to fail, or for an affliction to befall the Fae. This was attributed to the Cornerstone's incompleteness, and as a direct result of the Fallen's betrayal. But each time, the Fae would be able to band together and revive the stone to keep it from falling.
The Cornerstone was jealously guarded by the Knights Primevals, named for the Primeval Races who had sacrificed themselves for the safety and stability of Aradeyl. They built a fortress around the Cornerstone, and for centuries, would ensure no one got past their defences to harm the Cornerstone again. Then one day, their defences slipped, and Aradeyl paid the ultimate price for it.