Cosmologists found evidence of portals between the Abyss and the Barrens of Doom and Despair, Clangor, the Demonweb Pits, and Hammergrim, with intermittent portals to Deep Caverns and Fated Depths. When the Great Wheel model was replaced by the World Tree cosmology model, the river Styx was renamed the River of Blood and it flowed through all the fiendish planes (except for the Supreme Throne and the Demonweb Pits) originating in the Abyss, passing through the Blood Rift-an unusual plane that connected the Abyss with the Nine Hells -bringing the demons even closer to their arch-enemies the devils, resulting in the Blood War. Some branches of the Styx flowed down the holes (which were conduits to the various layers) and some of these holes supplied water to the Styx in reverse waterfalls.
The first layer, named Pazunia after the demon lord Pazuzu, was described as a barren, dusty place baking under a red sun, broken only by great iron fortresses, huge holes in the ground, and the river Styx. It was possible that the number of layers was infinite, but no one could be certain. Some estimated that the Abyss had 666 layers, while the Fraternity of Order claimed to have catalogued 679 layers.
In the Great Wheel cosmology model, the Abyss was an Outer plane on the Great Wheel connected to the Astral plane, Pandemonium, Carceri, and the Outlands. 6.2.8 Organized Play & Licensed Adventures.
