This event is mentioned in several places. The overall story will be gathered here.
Eru, the creator god, gradually grew uninvolved with the world after the fourth age. Other beings began to amass great power, receive worship from mortals, and call themselves gods. This went on for millennia, until there was a very large number of beings like this - fourteen different groups of related gods, with more than a hundred supposedly divine beings.
In the middle 1150s, Eru apparently awoke, and began to take an interest in this situation. He seemed displeased with these upstart beings, and began arming a number of his followers, creations, and allies with power he granted them directly, to take his cause to the world. He also led a number of attacks on the home planes of many of these beings, wiping out a great number of them. This led to the survivors banding together for self-preservation.
The events came to a head in September 1161.
JUDGEMENT DAY - THE FINAL BATTLE (Actual date - March 19, 1997)
The final battle between the Eru forces and the armies of all the surviving gods was a coup for the younger gods. Eru, convinced that the three alliances would not fight together, planned to attack the first group three days after the attack on the Celtic temples. The armies from the first group arranged themselves on battlefields all over the cosmos at the appointed time, and waited. Soon enough, the warriors of Eru appeared, their ranks bolstered by deva-like beings, devils, demons, and the servants of gods who had sworn their allegiance to Eru. They were ambushed by forces from the other two groups, who arrived at the same time, which caused momentary confusion until the human temples saw the demons and devils and such attacking the Eru forces.
Note that magical flight, dimension door, and teleportation out of (and around) the battle area did not work (although some were able to teleport in). This effect covered an area nearly a mile across. Winged flight will work normally. However, until the battle ends, only relic-level power allowed escape out of the area.
Near Aertael, on an ancient battlefield, the forces of the country arrayed themselves. They were beset by a similarly large army of Eru's forces, joined by Alastor, the god of berserk battle. Alastor plummeted out of the sky, actually landing on and killing Drius, henchman of Augustus.
The battle was vicious, quick and brutal, as combats between high level warriors tend to be. In the end, the field lay covered in corpses, and Eru had been defeated. News from the messengers of the surviving gods indicated that Eru had been destroyed by a massed attack of gods and their servants.
Casualties of the gods included Alastor, Huitzilopochtli, Thoth, Apshai, Morrigan, Anu, Vidar, the Fenris wolf, Camazotz, Poseidon, Forseti, Enlil, Prometheus, Seker, Surma, Utu, Tlaloc, and Nergal. Also, many of the humanoid gods were slain, but since little is really known of them by humans and demi-humans, their fates are not listed.
Others, recognizable by the party, fighting nearby were:
Thege's group: Thege, Levan, Kelvar, Rigdaur, Wevlin, Bridana, Xeriah, Imara, Rand, Iliea, Orestes, Miramar, Norri, Quinlin, Drius, Periahn and Fen Yasuko.
Government group: Findel, Hawk, Mikka, Thulemar, Felimid, Khazad, Aramar, Dandir, Bekka, Venetia.
Finarfin group: Finarfin, young Alterein, Airlaen, Hirlaen, a number of unnamed warriors.
The king's personal bodyguard/assassin.
The high priest of Thor, the female with Doombringer.
Bregelad, riding a vulture lion, with other lions around him.
Ivanslop, Tim, and a number of supposedly "retired" characters are seen at various times.
A large contingent from the Set temple, with Mourngrym (undead, possibly), a Death Slaad.
Venetia, glowing bright like the sun, attacking like a whirlwind, striking every segment! Sometimes she strikes allies, performing a Heal upon them when doing so.
A small number of angelic looking beings - devas? Which are difficult to look at, even for the most Good.
Surprises: A white-armored person appears, with a brilliant white two-handed sword (recognizable to some as Stormbreaker). He is trying to get to Alastor; many warriors get in his way. One hit invariably slays them, sometimes two at a time. Finally, he reaches Alastor; they wound each other, Alastor stumbles away, and both die. The white-armored man is found to be Shadow. Only artifact level healing can bring him back from the dead. Alastor's body consumes itself and all he carries within seconds, leaving a crater fifty feet across. Rolan asks that Shadow's body be placed on his back, and he says that Yfandes can call him back when a way to heal Shadow is found. (Note that Shadow can be raised, but he would die again within seconds, as his wound will not heal and is mortal.)
Cirle', the emperor of Calendriahn, is seen across the field. He is a huge, muscular black man, who weilds Stormbringer. He is unable to reach Alastor, and leaves when Alastor dies.
A white-haired woman, accompanied by two children which shapeshift into all sorts of animal and even energy forms, kills by a touch. If approached, she will say her name is Brann, and the children are Jaril and Yaril, the children of the Mountain. They are some sort of powerful spirits, and she feeds them the life energies of those she kills. They cannot take this energy for themselves. She is four hundred years old, but looks twenty.
Energy bombs from Eru warriors elsewhere on the field will strike randomly among the party several times per round.
Among those also slain by Alastor: Thege, Rigdaur, Imara, Rand (revealed to be Bradnar), Norri, Drius. Their bodies are claimed by their family, friends, or in Bradnar's case, the government (he has a will).
Fighting on Alastor's side, slain by Shadow (of importance): Mormar, Malivona.
Slain, fighting on the temples' side: the animated (?) body of Mourngrym. He is destroyed by Alastor. A Death Slaad, killed defending the high priest of Set.
High priests who are slain: all of those of gods which die (most are slain at the moment of their gods' deaths, having lived long past their normal lifespans; their temples reclaim their possessions). Others slain permanently: Heimdall, Shu, Aegir, Isis, Sif, Hanali, Hephaestus, Dunatis, Tuoni, Surtur, Hades, Tezcatlipoca.
A young man, dressed in ranger garb, soft brown leathers, with a short bow and short swords, introduces himself as Skydancer. He has long, black hair, is very tall - 7', 400 lbs., probably a natural 19 strength. He says he is a friend of Shadow's, "from the homelands," and tells that the Donblas temple (which recovered Stormbreaker just days ago) asked him to weild it against Alastor. The sword is reclaimed by the Donblas temple, and Shadow and all his gear have gone with Rolan. However, he says that Shadow can be healed, with artifact level magic, but if raised will immediately die again; Rolan will return with Shadow's body if summoned.
At the feet of each survivor, and next to the body of each of the slain, appears a lump of meteorite. It feels soft and pliable, and can be molded. Each person, upon touching the lump, realizes that it will become a +6 item of whatever weapon, armor or protection device they desire, and that they have been provided by the surviving gods as a measure of their gratitude. They can be molded only by the owner; note this is a magical process and requires no skill. These items will function within anti-magic shells, due to their divine origin.
The surviving gods are listed on the Deities page.