- Numidium was Tiber Septim's secret weapon in his bid for supreme power: a thousand foot tall automaton, a golem or an atronach of sorts powered by a gem called the Mantella. — A letter received by the Hero of Daggerfall
The Numidium or Anumidum, also known as the Brass God or the Brass Tower, was a gigantic golem of Dwemer origin. Constructed by Tonal Architect Lord Kagrenac, Numidium was directly related to the disappearance of the Dwemer, and since then has been resurrected several times.
By the end of the Second Era, the Morrowind Tribunal had possession of Numidium. As a part of the Armistice with the Empire, the Tribunal gave Tiber Septim the golem. The Numidium was first reactivated by Tiber based on Zurin Arctus' Dwemer research. Reactivating the Numidium required a replacement heart, for which the Mantella was used, a soul gem that mimicked the properties of Lorkhan's Heart when filled with the soul of a Shezarrine. The golem was controlled by a Totem that can only be wielded by those of royal blood or great power.
The Numidium proved very effective in bringing down the mighty Aldmeri Dominion and conquering Tamriel in 2E 896. The official records tell a story wherein after defeating all his enemies, Tiber Septim used the Numidium to destroy the neutral royal families of Tamriel so that he could enthrone persons he knew to be loyal. The Underking, another Shezarrine who was confused for Zurin Arctus due to their shared soul, disagreed with this use of the Numidium, and tried to reclaim the Mantella. However, the process devastated both Numidium and the Underking. The heart they shared was blown into Aetherius. Pieces of the Numidium were scattered throughout Tamriel.
In the centuries that followed, the Blades were entrusted with the task of collecting the pieces of the Numidium. During the reign of Uriel Septim VII, both the Numidium and the Totem were found in the Iliac Bay region. This nearly set off a civil war amongst the dozens of independent city-states in the region, beginning with the murder of King Lysandus of Daggerfall. Ultimately, an anonymous hero traveled to the plane of Aetherius to recover the Mantella, then returned to Mundus and activated the Numidium, resulting with the Warp in the West and Numidium's subsequent destruction.
A similar Dwemer brass golem, known as Akulakhan or the Second Numidium, was built by Dagoth Ur in his plans to drive the foreigners out of Morrowind and then conquer Tamriel. Akulakhan was inspired by Kagrenac's theories and powered by the Heart of Lorkhan. It was destroyed by the Nerevarine in 3E 427.