The Numidium, also known as the Brass God or Brass Tower, is a colossal humanoid golem created by the Dwemer, said to have been a thousand feet tall. Two installments of The Elder Scrolls series, The Elder Scrolls II: Daggerfall and The Elder Scrolls III: Morrowind, involve the Numidium, or at least its concept, as a central element in their stories.
First Numidium (Anumidium)
The Numidium was designed by Kagrenac, a Dwemer Tonal Architect during the First Era, and was intended to serve as a god of sorts for the Dwemer people. There are many theories that propose that it was built to allow for the mortal plane's transcendence. The original power source was the Heart of Lorkhan, whose power the Dwemer had accessed using Kagrenac's Tools: Keening, Sunder, and Wraithguard. It was first used in the Battle of Red Mountain, when Chimer forces assailed the Dwemer stronghold and captured it after the mysterious disappearance of the Dwemer.
The Numidium was gifted to Tiber Septim by the Tribunal in return for Morrowind's semi-autonomy during his conquest of Tamriel. The Emperor ordered his Imperial Battlemage, Zurin Arctus, to construct a control device known as the Totem of Tiber Septim. The Tribunal did not include the Heart as a power source, due to it being the source of their divine power, so a new one called the Mantella was created and infused with a powerful life energy. The Numidium was used by Tiber Septim to subjugate all of Tamriel, including the neutral Tamrielic royal families, in an attempt to eliminate anyone not absolutely loyal to his rule. An enraged Zurin Arctus attempted to halt the Emperor's mad conquest, and in the ensuing chaos, the Mantella was lost and left the Numidium shattered.
During the events of The Elder Scrolls II: Daggerfall, the Mantella is recovered, and the Numidium is activated by an unknown person. As a result, a "Dragon Break" (a spacetime anomaly) occurs. Subsequently, multiple endings of Daggerfall occur simultaneously: the Kings of Iliac Bay are defeated, preventing a major war; Orcs become citizens of the Empire; Mannimarco, the King of Worms becomes a god; the Underking is laid to rest; and the Numidium itself is destroyed.
Second Numidium (Akulakhan)
During the events of The Elder Scrolls III: Morrowind, the second Numidium, named Akulakhan, is a partial reconstruction of the first Numidium and is powered by the Heart of Lorkhan. Its construction was overseen by the maddened Dagoth Ur, whose goal is to cover the entirety of the world with his Blight, a deadly disease that he uses to infect, convert, and control the citizens of Morrowind, so all mortals might be connected to the Heart and thus be controlled by Dagoth Ur.
However, in 3E 427, the Nerevarine arrives in Vvardenfell from the Imperial City prison, guided by Vivec, they recover Kagrenac's Tools and journey to the Red Mountain's fortress to defeat Dagoth Ur. Using the power of the tools, the Nerevarine is able to destroy the enchantments on the Heart, killing Dagoth Ur and destroying Akulakhan.
- The Numidium is referenced in the Prophecy of the Dragonborn as the "Brass Tower" and is shown on Alduin's Wall.
- In The Elder Scrolls Online, Sheogorath mentions reassembling the Numidium to the Vestige, around 300 years prior to its use by Tiber Septim and around 750 years prior to it being rebuilt by Dagoth Ur.
- After the Dwemer's disappearance, the Numidium's blueprints were kept in Coldharbour's Library of Dusk until around the time of the Planemeld, when they were stolen by an unknown assailant.
- The Numidium can essentially be considered a much larger Dwarven Centurion; it appears to be crafted of the same metal, requires a significant power source, has generally the same face on its "head," and can be controlled by its master.
- The Elder Scrolls II: Daggerfall
- The Elder Scrolls III: Morrowind
- The Elder Scrolls V: Skyrim (mentioned only) 
- The Elder Scrolls V: Dragonborn (mentioned only)
- The Elder Scrolls Online (mentioned only)
- The Book of the Dragonborn
- Dialogue with Baladas Demnevanni and Yagrum Bagarn
- Letter from the Thieves Guild
- Dialogue with Yagrum Bagarn
- Progress of Truth
- Kagrenac's Tools
- Dialogue with Vivec
- Anonymous Letters
- The Arcturian Heresy
- Endings of The Elder Scrolls II: Daggerfall
- Dagoth Ur's Plans
- Events in The Elder Scrolls III: Morrowind