Machine-heart

The "machine-heart" was the system of machinery built on the Homeworld itself to effect the anchoring of the thread, connecting to the proto-timeships positioned at strategic points through time to lock in the structure of history.

On the actual day of the ceremony, representatives of the Ruling Houses gathered at the machine-heart to connect their respective Houses' biodata to history forever. (PROSE: The Book of the War) The obelisk of the Eye of Harmony was at the centre of the ceremony, still out in the open, with Rassilon himself standing in front of it with the Great Key of Rassilon held aloft. As he "claimed stewardship of Time", Rassilon used the Key to activate the Eye to achieve "universal consistency". (COMIC: The Final Chapter)

However, as the anchoring was effected, one of the Yssgaroth burst through from another reality at the machine-heart. It destroyed the machinery and likely wiped out most of the lords in attendance, creating the caldera. (PROSE: The Book of the War)