Obelisk of Rassilon

The Obelisk of Rassilon (AUDIO: Renaissance) was the "mast" constructed by Rassilon through which the power of the Eye of Harmony was channeled.

The mast was worked into an "endlessly dynamic equation" via being balanced with the mass of Gallifrey itself: should it be removed from Gallifrey, the whole planet's matter would turn to anti-matter. (PROSE: The Legacy of Gallifrey) The obelisk took centre-stage in the ceremony through which the Gallifreyans officially became Time Lords as Rassilon used the Great Key to "activate" the Eye, (COMIC: The Final Chapter) effecting the anchoring of the thread. The system at whose heart the ceremony was held was known as the machine-heart.

During the ceremony, the Yssgaroth emerged, wrecking the machinery and creating the caldera in its place, a space-time anomaly (PROSE: The Book of the War) whose heart would come to be known as the Untempered Schism. (PROSE: Tempered, TV: The Sound of Drums) In later eras, the citadel was built up over the site of the caldera, which became a "womb"-like crypt of sorts; (PROSE: The Book of the War) the obelisk was embedded directly beneath the Panopticon, with a mechanism activated by the Rod of Rassilon allowing it to be raised into the centre of the Panopticon if necessary.

By the Fourth Doctor's lifetime, this capacity had passed into myth until it was rediscovered by and Goth. After arranging the murder of the President to lay his hands on the Rod and the protective Sash of Rassilon, the Master summoned up the obelisk and began unhooking the systems keeping the power of the Eye contained, intending to absorb them himself so as to acquire a new regenerative cycle as well as "complete power" over "all matter" in the cosmos. The Fourth Doctor stopped him before he could completely free the obelisk from its restraints, and the power of the Eye was covered once again. (TV: The Deadly Assassin)