Eons ago. several powerful tanar'ri tricked a dozen astral devas - each the powerful agent of a good deity - into visiting the Abyss for a council ot peace. The Upper Planes had watched nervously as the former slaves overthrew their obyrith masters, and several celestial powers sought to play a role in the emerging Abyssal landscape. After a brief challenge to the devas' masters, the demons bound the envoys to the towering trunks of twelve mighty trees in a desolate layer, sacrificing them in a vile arcane ritual that forever infused the layer with evil energies.
The devas' shattering death-screams still haunt the layer, now known as Twelvetrees. A massive basalt platform now commemorates the site of the original sacrifice, ringed by sickly pines that still ooze spiritual slime in an echo oi the blood spilled by the ancient devas. Tanar'ri from throughout the Abyss make the pilgrimage to Twelvetrees in memory of their defiant ancestors, many hoping to use the platform to infuse their own infernal plots and rituals. Nearly all tanar'ri rhroughour the multiverse know of and respect the power of Twelvetrees, and an aflront to the layer is an affront to demons everywhere.
The palpable evil of Twelvetrees is like a drug to the pilgrims drawn to the layer, who count among their ranks several mariliths, nalfeshnees, vrocks, and hezrous. Most are half-demons, drerches, and rurrerkin, desperate beings grasping for a path to a new form and greater power. These creatures bask in a euphoric haze of religious ecstasy and pay lirtle attention to the world around rhem. Nondemonic visitors often find it surprisingly easy to wander about the layer, needing only to avoid the chasmes that patrol the layer from the skies and the handful of kelvezus who zealously wander the crowds in search of imposrors to murder.
Huge skeletal scaffolds loom over the landscape, supporting a massive dock structure used by a consortium of demons and members of the Doomguard planar faction to create ships of chaos, Six of these flying dreadnoughts - capable of moving from plane to plane - have been completed within the past decade. A seventh nears completion high above the Twelvetrees site, its half-finished deck a torrent ot flying demons, writhing larvae, and eldritch energies. The dark clouds above roil with thunder and flashes of lightning.