The 12th layer of the Abyss is a place where the tanar'ri conduct necromantic magics and other vile projects for their Blood War with the devils of the Nine Hells.
It is said a long time ago, twelve devas were captured by the fiends and sacrificed here. Their screams still echo and resound throughout the layer, not unlike the roaring madness of Pandemonium. Those without telepathic capabilities like the tanar'ri are hard pressed to communicate with one another because of the incessant shrieking.
The layer itself is simple bare rock but the tanar'ri had built titanic scaffoldings too numerous to count which dominate the otherwise sparse landscape. Here, they build their necromantic Blood War engines, the foremost of which are the infamous Ships of Chaos.
The Ship of Chaos are among the latest triumph concocted by brilliant and yet twisted minds of Blood War generals. Built from bones, larvae, spirits, unidentified gunk, and yet more larvae, each ship is guided by the intelligence of a vrock demon melded into it. The Ships use the larvae trapped in their hulls as fuel as they glide across the Lower Planes. They are equipped with several offensive capabilities, including ballistae fitted in each "mouth" of the ship's two "heads". Each ship also generates an entropic field which is particularly effective in disrupting the regimented ranks of the devils.