When I was a teenager, over 35 years ago, I created a world in which the nation of Pesh (yeah, I lifted the name Pesh, it being a sort of United States of America of Elfdom) had been annihilated in a meteor shower by various Demons bent on destroying that country and it's people.
The Elves had been practically annihilated and those that survived fled South and across the ocean. Very few stuck around. But some few went North.
Pesh was a huge country and after being leveled the peoples of the Northern nations (mostly human with a few dwarves) never tried again to cross Pesh (both because of the devastation and because of the fear of what might happen to them) and so were cut off geographically from the South, and East. The sea was to the West but they didn't sail too far across it for fear of either encountering the surviving Elves or for fear of encountering whoever or whatever had destroyed the Elves.
The country though did have ruins that survived the meteor and resulting firestorm. In the ruins of one city, the old Capital, also named Pesh, they found a Temple. The temple was spherical in shape, white and looked like smooth chalk, was half-buried, rotated, had been protected from destruction by powerful magics and artifacts and relics, and was connected with both the old national Library and a tesseract.
The party penetrated the Temple, found the Fables of Burdoch (which I had written out in book form and partially burned so that 7 of the Fables still could be read - back then I created a lot of props), and with those Fables they were led to various clues about famous Peshian artifacts and relics and magical devices, such as the Rod of 7 Parts. Which the cleric eventually recovered.
One fable led to the underground crypt of the most famous Elven Paladin (who had lived 2000 years before, 500 years before the destruction of Pesh - he was credited with binding the horde of Demons who had escaped and eventually destroyed Pesh) of Pesh's history and when the party arrived there and discovered the crypt the Paladin's skeleton stood up and walked straight for the party's Paladin (who was distantly Half-Eleven). The party Paladin thought he was under attack by a powerful Undead creature, and tried to turn the Elf, but right as the dead Eleven reached him the skeleton slipped out of his armor and weapons and his skeleton fell to ashes, but his ghost entered the party Paladin's body. (Though the Paladin did not know that at the time and I sometimes wonder if the players ever figured out he had become "possessed" by the dead Elf).
The party came to realize that the Armor and Arms of the Dead Elven Paladin were meant to be taken up by the party Paladin. The Armor was Green and Blue and each separate piece was a relic and could do certain things (though the Paladin had to learn how each piece operated, and even by his death had not discovered everything the Armor could do). The sword was a +5 Holy Avenger (back then everything magical had a "+" score, now I don't use number scores, but then I did) and was +7 against Demons of all kinds. It could also, if used right, bind Demons to the user's will, and do all kinds of things (it was a Relic as well) and allowed the Ghost of the Dead Elf to communicate with the party Paladin under certain conditions. The sword seemed to have a personality of it's own, but it was actually the Dead Elf Paladin working through the sword.
The Sword was named, "Wrothcholire" which meant "The Blood Fury," among other things. I patterned it partially after Caliburn, Arthur's sword, and partially after Durandal, Roland's sword. It was a very potent weapon against evil, and Demons in particular. There were a lot of excellent fights, quests, and adventures involving that Paladin, his relical Armor and Wrothcholire.
Finally the Paladin sacrificed himself so that the party's Cleric and Wizard (twin brothers) could reach a device in Pesh that would annihilate the Demons once and for all, for they had returned upon learning of the Party and their activities in Pesh. The Cleric and Wizard used their magic to activate the device which annihilated the Demons. But not before the demons had slain the Paladin. But from where the Paladin's blood had soaked an altar vegetation started to grow (none had grown in Pesh since the meteor attack, it was all sand and clay desert) and eventually (within a few years) the whole country was rejuvenated and flourishing again. Producing crops and the 3 great rivers were flowing again. It became the new home of Men and Half-Elves.
The Cleric and Wizard and surviving party members retired or went into self-imposed exile, their children or relatives became a second generation of adventurers, the party Paladin (who never sired children) was buried beside the Eleven Paladin, and neither the armor nor Wrothcholire were ever found.
Though it took about three years in real time to play out, that was a good campaign and the best Sword I ever invented for my players.