The layer's climate resembled the Elemental Plane of Fire. It was dominated by a scorching heat that ignited the air itself, creating seemingly sentient and aggressive flames that leapt at visitors but not at the residents. The ground had fissures that spewed jets of flame that flowed into rivers of liquid fire. It contained numerous volcanoes whose eruptive products flowed through rivers of lava into an incandescent ocean of magma.
The layer was the center of the judicial system of the Nine Hells. All legal disputes involving devils were discussed in the Diabolical Court, an independent institution under Belial's supervision that only answered to Asmodeus. It was also in Phlegethos that the promotion or demotion of devils took place, through a ritual that temporarily made them vulnerable to the layer's flames.
- Abriymoch, a city made of volcanic rock, obsidian, and crystal, located on the caldera of a volcano. It was said to have been built on top of the grave of a deity killed by Asmodeus. It contained numerous taverns and places for entertainment.
- Jealous Heart, realm of Inanna of the Untheric pantheon. A vast field of crimson dust and rivers of blood, it was not as physically hot as the rest of the layer, but it awakened an equally hot passion for war in its visitors and inhabitants.
- The Pit of Flame, a boiling lake at the center of the layer that served as a place of punishment and torment for devils that broke the law. It was operated by osyluths and guarded by numerous cornugons.
In addition to the vast hamatula and cornugon contingents, the layer was inhabited primarily by hell hounds, imps, and spinagons. Other planar creatures also made their home there, but the heavily guarded layer was not welcoming to strangers.
- ↑ 1.0 1.1 1.2 Chris Pramas (1999). Guide to Hell. (TSR, Inc.), p. 32. ISBN 978-0786914319.
- ↑ 2.0 2.1 2.2 Jeff Grubb, Bruce R. Cordell, David Noonan (September 2001). Manual of the Planes 3rd edition. (Wizards of the Coast), pp. 115, 119. ISBN 0-7869-1850-8.
- ↑ Richard Baker, John Rogers, Robert J. Schwalb, James Wyatt (December 2008). Manual of the Planes 4th edition. (Wizards of the Coast), pp. 97, 101–102. ISBN 978-0-7869-5002-7.
- ↑ Richard Baker, James Wyatt (March 2004). Player's Guide to Faerûn. (Wizards of the Coast), p. 161. ISBN 0-7869-3134-5.
- ↑ 5.0 5.1 Colin McComb (1996). On Hallowed Ground. Edited by Ray Vallese. (TSR, Inc), p. 172. ISBN 0-7869-0430-5.
- ↑ Robin D. Laws, Robert J. Schwalb (December 2006). Fiendish Codex II: Tyrants of the Nine Hells. (Wizards of the Coast), pp. 50–54. ISBN 0-7869-3940-0.
- ↑ 7.0 7.1 7.2 7.3 Mike Mearls, Jeremy Crawford (May 29, 2018). Mordenkainen's Tome of Foes. Edited by Kim Mohan, Michele Carter. (Wizards of the Coast), pp. 12–13. ISBN 978-0786966240.
- ↑ Eric L. Boyd (1997). Powers and Pantheons. (TSR, Inc), p. 95. ISBN 0-7869-0657-X.
- ↑ Colin McComb (1996). On Hallowed Ground. Edited by Ray Vallese. (TSR, Inc), p. 62. ISBN 0-7869-0430-5.