Atnium, or 'Elder City', is a safe-haven for Mer of all kinds, and is also the capital city of the Eltmer. It is a hidden island in-between Tamriel and the Summerset Isles, concealed by a very similar mist to the one that surrounds Pynandonea.
The High Priest of the Eltmer is the ruler of this island kingdom.
In 1E 2300, an Eltmer explorer by the name of Alir discovered this island, after forcing his way to the island using magic. The natives, which seemed to be Elf-like men, forced him out.
He fled back to the Eltmer kingdom of Artaeum, where he informed the High Priest of this land. This Eltmer Ruler, renowned as the most vicious and cruel of the era, immediately saw the uses of the island. He sent out expeditionary forces to the island, where the armies murdered and enslaved the native people.
Within a few years, the Royal Architect had founded a city, which he dubbed, 'Atnium.'
After its founding, the city of Atnium grew into a beautiful kingdom, which the Elves of Tamriel would call the 'Jewel of the Seas.' This city eventually became the Capital of the Eltmer lands, just before the disappearance of Artaeum.
After many long years of servitude, the native people revolted, attacking their Elven Masters. They used boats to flee into the sea, where they formed their own island kingdom, a bit away. The native people began the Raiding of Atnium, which lasted for hundreds of years. The men would slide into the waterways of Atnium silently, and burn the city, in revenge.
The Eltmer eventually forsook their Oath of Peace, and retaliated, attacking the raiders and destroying them with their superior magic. When the Reman Dynasty attacked the Dunmer, the Eltmer appeared to help. They participated in no battles, but they invited the few Dunmer who were willing to come to Atnium.
Thus, the Era of the Grey began. The Dunmer People were not used to this calm, ocean life among the beautiful trees and plants of Atnium, and grew unsettled. A few Dunmer decided to try to form their own volcano, in the middle of the City. They ventured into the caves beneath the Island, and began to pray to Mephala, Boethia, and, surprisingly, Mehrunes Dagon.
The following explosion devastated Atnium, killing hundreds of Eltmer and Dunmer, and sinking the part of the Island that had been donated to the Dunmer. The Eltmer were enraged by the destruction of their beautiful island, and drove the Dunmer from their home. Thus, the Era of Reformation began.
The Eltmer slowly began the process of rebuilding their home. The Dunmer who had fled back to Morrowind spread the ruin of this kingdom to the other Mer, who became intrigued. Groups of Altmer, Bosmer, Orsimer, Maormer, and Dunmer slowly began to head towards Atnium, helping the Eltmer rebuild the beautiful island.
Eventually, the Eltmer allowed the other races to settle there, and the city finally became a city for Elves. Thus, the Era of Sanctuary began. The only Race of Mer not allowed onto the sprawling island city were the Balmer, and this caused them to be deeply offended. Because of this, the War of the Black Death began.
The first attack on the United City was an attempt at Invasion, a plan orchestrated between the Balmer and a few of the Dunmer who were still angry over the Eltmer's treatment of their fellow Dunmer, during the the Era of the Grey. The Eltmer beat this attack back.
The second attack was a sneak attack, upon a fleet of Maormer fishing ships leaving the harbor of the city. Many Maormer died, during this naval battle.
The third attack was a plague the Balmer created, which they placed in the city. The plague was so deadly, the city of Atnium lost half of its population.
The Eltmer were so enraged they flew out of their city and fell upon the Balmer, destroying the entire invasion force. The War of the Black Death was over. But the Balmer and the Eltmer have hated each other, ever since.
In the Fourth Era, the United City of Mer fought back an invasion from the Thalmor.
- The Current Leader of Atnium is actually of a mixed race, being half Dunmer and half Eltmer.
- Many Mer hate the United City, as they believe all of the races together, in one city, is an abomination.