The City of Brass was a city in The Elemental Plane of Fire, which served as a trade hub for the elemental planes. It contained The Elite Forge, a championship committee that could only be accessed by those who have gotten consent from Emperor Natar DuMonte, the leader of the City of Brass. He would only allow through those who have defeated leaders in each of the four elemental planes: wind, earth, fire, and water.
The Tower of Grey, on their mission to save the world, visited Ioun, goddess of knowledge, seeking information on The Orb, which was showing them images of location throughout The Multiverse. One of those locations was The City of Brass.