Project Revenant was a Time Lord project set up by the War Council during the Last Great Time War. Its purpose was to resurrect the "most brilliant minds Gallifrey [had] ever seen" from the Matrix in order to win the Last Great Time War against the Daleks. As part of the project, its members (AUDIO: Celestial Intervention, Desperate Measures) made contact with Rassilon himself and encouraged him to return to the physical world for the War. (PROSE: Engines of War)
The Project was housed in a pocket dimension linked to Gallifrey in the Death Zone. (AUDIO: Celestial Intervention) Two months into the war, the Daleks discovered Project Revenant and a Supreme led an invasion of the dimension, planning to use the Project for their own ends. The War Council committed increasing amount of forces to defend the facility, but the Daleks kept advancing.
Concerned the Daleks could gain access to Gallifrey through the facility, Coordinator Romana II dispatched Narvin and Karla to destroy the facility and collapse the dimension with the Daleks inside. However Karla betrayed Narvin and stole the facility’s power core, taking it into the Matrix to enable the resurrection of Rassilon, whose Matrix projection had to be retrieved from deep in the Matrix. Narvin was rescued from the facility moments before the detonation by Braxiatel in his TARDIS. The facility was destroyed as planned, collapsing the pocket dimension which killed all the invading Daleks, including the Supreme.
Rassilon's resurrection was achieved as planned when his Matrix projection was imprinted onto the Time Lord Valerian, killing Valerian in the process. (AUDIO: Desperate Measures)