Also known as the Hammer of Gharen, with which it is twinned.
The Anvil of Mithas is an ancient anvil created by Mithas, the greatest Dwemer smith. It is twinned with the Hammer of Gharen, which is the only object strong enough not to shatter when used to shape metal upon the Anvil. When the Hammer strikes the Anvil, it produces a ringing which reveals the location of the entrance to the Dwarven mines beneath Red Mountain.
By the time of the Imperial Simulacrum, the Anvil had come into the possession of King of Ebonheart. The King had the Eternal Champion bring him the Hammer, which had been lost in the dungeon known as Black Gate, and used the artifacts to craft the finest armor and weapons in the realm. The Anvil has never reportedly left the city’s palace since.
Smithing tests performed while utilizing the paired Hammer and Anvil receive a +20 bonus, and any item crafted raises its maximum number of modifications by 1. (Book of Circles pg. 21).