This massive landmark of actual skulls represents devilish trophies taken in the Blood War. Most of the trophies are twisted, demonic skulls, varying in size from minuscule to the size of a house. The pillar rises to a height of more than a mile.
The Pillar stands near the part of the ledge where access to the next lower layer is an easy walk down a particularly tall metal spire of the city Dis reaching up through the haze between layers. This spire sees quite a bit of devil and petitioner traffic on its spiral stairwell - and quite a few accidental and not-so-accidental falls. However, a massive cave mouth near the base of the pillar of Skulls holds a particularly terrible sentinel of the ledge: Tiamat.
It has long been rumored that the skulls themselves con- tain some magical power. Some say that they are enchanted and can be fashioned into impregnable armor, while others say that if properly treated with alchemical elixirs, they become highly unstable and explode upon even the slightest impact. None of these rumors is true, but enough treasure seekers have come skulking around the pillar that a cadre of osyluths has been assigned to stand guard. They will attack anyone they catch approaching the Pillar of Skulls, no matter how outmatched they might be - they fear Tiamat’s retribution more than they do death in battle.
The Pillar of Skulls is a planar touchstone, granting abilities to fight tanar'ri to those who know its secrets.