Time travel gave Salomon the chance to access certain hidden histories. In particular, his cooperation and conflicts with the Eternals gradually refined his research into immortals, allowing him to learn things that even few within the Eternals themselves knew.
Circe—also known as Cersei—the witch born from the fusion of the Eternals and the Olympian Pantheon.
She told the Emperor the secret of the Earth Machine.
When the Emperor first came into contact with the Eternals, the Earth Machine, the important machine created by the Celestial race, had only its Rebirth Chamber left. The other components had been taken away by the Asgardians as spoils of war. Using the Rebirth Chamber and the remaining components, the Eternals built the Olympus System. Over the years, the components taken by the Asgardians became part of the Asgardian Supreme Throne, the Rainbow Bridge Modulator, and Valhalla.
Now Salomon intended to take those components, along with the Asgardians' research into the Earth Machine, and restore part of its functions. He had already dismantled and studied the Eternals' Rebirth Chamber, which helped him gather the souls of Gene-modded Warriors in the Outer Dimensions—the Asgardians had also studied the Rebirth Chamber. Odin's ancestors used the results of that research and the Runic system developed by the Vanir to create Valhalla and Niflheim.
The Asgardians attempted to find a way to isolate the Material Universe from the Outer Dimensions, denying the shadows of the Outer Dimensions the opportunity to draw power from Asgard. They also used it to select the souls of powerful warriors in preparation for the final war. But Odin's ancestors had been too optimistic. They believed they could completely absorb Celestial race technology and rebuild a Rebirth Chamber entirely belonging to Asgard.
Lacking the necessary equipment and knowledge, the Asgardians' experiment had undoubtedly failed.
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