Vethlanoril was an immense, highly advanced drow city in the far eastern reaches of The Underdark.
Famed not only for its powerful wizards and the architectural wonders of which they were capable, the city served to many as an example of what could be accomplished through the rejection of Lolth and her endlessly destructive influences.
Lolth would sadly have the final say in the matter, as Vethlanoril was destroyed in the wake of arcane warfare with its sister-city Siravassiryn after Lolth introduced each to The Shard of Pandemonium.
Vethlanoril was founded by a group of roughly two hundred dark elves. According to legend, they were fleeing a duergar insurrection in their previous home--an insurrection fomented by Lolth herself for the purposes of "testing allegiance in the wake of cruelty"
The names of these dark elves have been long forgotten, as was their shared desire. They insisted the city itself should be the only the only memory of them worthy of persisting, and so it was.
Vethlanoril was ultimately responsible for producing some of the most powerful drow wizards in history, perhaps most famously Arkaryvos.
In his final act, Arkaryvos legendarily sealed and banished The Shard of Pandemonium from the Underdark. Tragically, however, his heroism came too late to save either Vethlanoril or Siravassiryn from their mutual destruction.
Not one to let bygones be bygones, Lolth was unspeakably furious to learn of the rise of Siravassiryn (and its neighbor Vethlanoril) during her infamous Silence. Recognizing the power these two peaceful cities had amassed (and perhaps at the time considering it beyond her ability to directly intervene), Lolth decided to pit them against one another.
Having been given the Shard of Pandemonium as gift from Graz'zt, it took little more than placing it in a cavern equidistant from either city. She then enlisted spies to spread rumors about a powerful artifact before it was ultimately found by Mournas Oussana of Siravassiryn.
The Shard itself is imbued with uncontrollable Wild Magic and the unmistakeable evil that permeates The Abyss from which it was formed. It corrupts all who wield it, but not before grantimg them incredible, destructive and chaotic abilities. Plunged deftly into the heart of a city of gifted arcanists, it was only a matter of time before the city began to eat itself from within.
Vethlanoril's attempts to intervene were met with unmitigated animosity by a city already reeling from internal conflict, and the only thing that proved capable of uniting the Siravassiryne was a crusade against their once sister city. It is unknown how frequently the Shard changed hands once the conflict began, but the arcane warfare that followed its influence was enough to destroy both cities entirely.