During Tiber Septim's conquests at the end of the Second Era, Zurin Arctus brokered the agreement between Morrowind and Cyrodiil, preventing the war and making the Tribunal accept the laws of Tiber Septim. The agreement also gave the Numidium to the Septim Empire. Zurin Arctus was the one in charge of the research to reanimate the giant Dwemeri construct in order to use it as an ultimate weapon to crush the Aldmeri Dominion.
Arctus created the Totem of Tiber Septim to control the construct. He then created a powerful gem called the Mantella and infused his own heart into the gem. He then used the gem to power the Numidium. With this, the Altmer were eventually subdued, and Tiber Septim had conquered all of Tamriel.
Then Tiber Septim used the Numidium to crush the neutral royal families of Tamriel so that he could enthrone only people he knew to be loyal. Zurin Arctus was furious at this use. He then confronted Tiber Septim to reclaim the Mantella. During the Battle neither side won. The Mantella was blown out of Mundus and into Aetherius. The Numidium's body was scattered throughout Tamriel, and Arctus, without his life force, died.