The Doom that came to Wieland

Lying at the banks of Lake Geneva in rocky soil is the ancient city of Wieland run by an older branch of High Alfar (Elves) that had left Alfheinr centuries before. Making their way into the northern parts of the Alps, the tribe came across a lake that had recently been visited by the early Halstad Celts. Seeing the tribes as friendly enough, they camped near the edge of the same lake far away from the Halstad tribes so as not to bother them, then set about building a city out of local stone.
Over the years the city expanded into a maginificent wonderous place of commerce. Many different local tribes of Celts visited Weiland to buy & sell goods, and trade with the High Elves. Both protected each other and used the lake for religious purposes and for food.
This was to change in time with the arrival of the Romans. The fighting style of the Roman Legions overpowered the local Celtic forces and nearly done the same to Weiland.
Seeing the luxurious power & wealth of the High Elves was too much for Rome. The Senate demanded the city cut off and beseiged, wit hte Elves all killed or captured for use as slaves, preferably the former. The remains of the Celts at this time had fled into the mountains with a large contingent of them fleeing into the city itself. This had put the Weiland into a more desparate position, though they wouldn't turn their backs on their allies & frriends.
The Elves decided to try one last desparate gamble before they fell. Approaching the Celts, they knew that the lake was ised to bury the dead of many of the tribespeople. With this knowledge they asked the Celts if they could raise the dead in a gamble that would see such an army rise from the depth at the back of a part of the seige and break the Romans overall.
This led to outcries by the seers that led the religious orders of the Elves, and the Druids of the Celts. They were acred dead that would be reborn in time, but needed to remain in the watery grave of Lake Geneva in the meantime. The Vanir warned the Elves that their city would be cursed if they tampered with the dead belonging to the worshippers of another pantheon of deities. And the Druids warned their own deities looked at such an act as blasphemous and would in their turn, open the gates so to speak to Weiland while cursing the city to act like a warning against disturbing the dead.
Eventually the seige was nearly over and the Elves in their hubris, pushed on with their plan knowing they were doomed. Casting necromantic spells on a grand scale, an army of the dead proceeded to rise from Lake Geneva and swiftly beat back the Romans. And then the inevitable happened.
The dead were enraged they had been awoke and could not be born again to other brave Celts whilst the source of this magic still existed. They attacked the now severly damaged gates, tearing down the last remnants of the guards, and burned the city. Every living thing was slaughtered, and the treasuries, the temples, and all great buildings were damaged beyond repair. The dead themselves returned to the lake and went back to their graves.
Only death remained and the pall of death hung over Weiland. Harly any part of it remains covered in time and gradually to disappear once & for all. The dead had also enacted a part of a curse by the gods on Weiland destroying it, but the day it was destroyed, it would return for 24 hours and be populated by the spirits of those who lost their lives. The city appears at these times like a ruined desolate place only fit for the dead who themselves appear as faded & battered as Weiland. Treasure hunters and those looking to make a name for themselves sometimes seek it out to see what they can make of the experience. Most say that the pallid air that resides here is unusually mournful & draining after a few hours.
One thing that has to be mentioned is the date. The rituals and destruction happened on a rather fateful day, none other than Friday the 13th.