Timeline

• The planes are first formed.
• The baernaloths come forth within the Grey Waste, the yugoloths created by them some time later.
• The River Styx grows from a minor trickle through the Lower Planes to a full-fledged planar path.
• Apomps, trying to duplicate the creation of the yugoloths, inadvertantly forms the gehreleths. Because of this failure, Apomps and his creations are exiled to Carceri.
• The Heart of Darkness is created by the General of Gehenna, the first ultraloth
• The influx of law and chaos purged by the Heart of Darkness is channeled into the larvae of the Grey Waste. These larvae are herded to Baator and the Abyss, forming the first baatezu and tanar'ri. The yugoloths keep a hold on the two races without their knowledge, through a being known as the Maeldur Et Kavurik.
• The baatezu and tanar'ri gain total ownership of their planes over the baatorians and osyluths respectively.
• The baernaloths withdraw from their positions as rulers of the yugoloths, leaving little evidence of their former existence.
• The Blood War begins when a party of baatezu explorers set out from Baator, encountering first the "weak-willed" and "foolish" yugoloths before pressing through Carceri to the Abyss, resulting in a mass slaughter. A group of tanar'ri set out at almost the same time, also briefly encountering the yugoloths before reaching Baator, where things proceed similarly.
• The Lords of the Nine and Princes of the Abyss first appear. Though some are initially deposed, both groups soon set up hierarchies of forms and powers amongst the others of their kind, so as to encourage infighting and reduce the chances of a true foe.
• The earliest records presently accessible to mortals begin to appear.
• The baatezu and tanar'ri begin exploring the planes outside the scope of the Blood War, discovering various portals and paths far beyond their home planes.
• The celestials marshal forces to send against the fiends, in an attempt at wiping them out. A force of archons and aasimon millions strong is sent into the Lower Planes, and though initially successful as both types of fiends are forced into a two-front war, the baatezu and tanar'ri soon join forces to fight against the celestial armies as one. Within a week, only 3,000 celestials are said to survive this conflict.
• Realizing that if they are to be successful, the celestials must focus on wiping out either one race of fiends or the other, a schism forms amongst their number between the lawful archons wishing to destroy the tanar'ri, and the chaotic aasimon wishing the end of the baatezu.
• The first powers come into existence.
• Though the evil powers initially begin aiding the fiends in the Blood War, after the death of one of the first gods of chaos to move into the fight, they largely withdraw, helping only through their proxies if helping at all.
• The Mask of the Pit gambit is attempted.
• Bel is given command of the armies of Avernus, after the extraordinarily successful Four-Cross.
• Petitioners begin arriving from the Prime, and fiends soon discover that those arriving in their own planes can be twisted into new fiends, allowing their numbers to grow for the first time since their creation.
• The fiends discover Sigil, as well as the presence of the Lady of Pain preventing its use as a launching point for planar invasion.
• The only near-successful attempt at displacing the Lady of Pain from her rule of Sigil is made by a mortal mage; though this attempt ultimately failed, the Lady herself was missing from the city for weeks after the conflict, assumedly recovering from the strain. The mage that attempted this coup was imprisoned in the depths of Pandemonium for his efforts.
• Active recruiting by the fiends on the Prime first begins, with both baatezu and tanar'ri trying to lure mortals over to their outlooks in life, so as to bring more petitioners to their planes in death.
  • As a result of this recruiting, the first cambions and alu-fiends come about, eventually followed by the first tieflings.
• The Lady of Pain begins Mazing people, rather than trapping their essences in black soul crystals in the lowest layer of Pandemonium.
• 10,000 years ago - Shekelor makes his ultimately-failed attempt at dethroning the Lady of Pain from Sigil, using the aid of the mage that tried such eons hence.
• The failed attempt by the Dark Eight to ferment dissent amongst the baatezu, known as the Rebellion of the Inferiors, occurs.
• The Ghoresh Chasm forms in the Grey Waste, displacing a yugoloth citadel.
• Skall founds the Dustmen.
• c. 1000 years ago - 12 factols appeal to the Lady of Pain at the current location of the Twelve Factols inn about halting the slow Sigilian take-over of the Expansionist faction. In response, the Lady mazes their factol, Vartus Timlin, and bars the Expansionists from the city. This faction dissolves soon after.
• 982 years ago - The Fraternity of Order is founded.
• 900+ years ago - The Bleak Cabal is founded.
• The Athar are founded.
• The faction known today as the Believers of the Source is founded.
• The Sign of One is founded.
• The Transcendent Order is founded.
• 700 years ago - The earliest known reference to what may be the modern day Revolutionary League.
• 700 years ago - The Society of Sensation is first formed, as a loose organization at this time rather than a faction.
• 630 years ago - The Great Upheaval occurs in Sigil.
  • The loose organization of the Sinkers evolves into the Doomguard.
  • The Mercykillers are formed from the merger of the Sons of Mercy and the Sodkillers.
  • The Society of Sensation coalesces into a true faction.
  • The shakeup caused by the Upheaval inflates the membership of the Indeps to almost one million.
• ~600 years ago - Worried about being unable to control such a large organization of so many disparate views, the Lady brings about the death of nearly the entirety of the Indeps, bringing it down to 20,000. Today, most believe the deaths to be the result of a plague..
• 500 years ago - The Harmonium are founded on the prime world of Ortho.
• 150 years ago - The first reference to the Xaositects under their current name, though references to them under other names can be found dating back centuries.
• Orcus is slain by the Drow demigoddess Kiaransalee. She proceeds to wipe all mention of his name from all records throughout the multiverse, and has two of her servants hide his wand in the depths of Pandemonium.
• The tanar'ri, working alongside the Doomguard, work to create the first Ships of Chaos.