The Death Zone was an area of Gallifrey used during the Dark Time when Time Lords pitted combatants against each other in the "Game of Rassilon".
History
The Time Lords had used the Time Scoop to pull beings out of time and place them in the Death Zone, where they would play "the Game" and try to destroy each other. Daleks and Cybermen were never allowed because they played too well. According to the official history, Rassilon himself put a stop to the Game. From a control room located within the Capitol, only accessible by playing the right tune on the Harp of Rassilon, a person could activate and use the time scoop to capture beings.
When a being had been captured, a figure of them would be created and the figure would be placed somewhere on a model of the Zone, and wherever the figure was placed was where the being would materialise. From the Capitol, the High Council possessed a secret transmat system that was linked to the Death Zone and to the Tomb of Rassilon, which was located in the Zone. However, the transmat system needed activation from the Tomb of Rassilon side, so for a time it remained inaccessible.
Lord President Borusa re-activated the Death Zone. Not knowing Borusa's treachery and only that a Game of Rassilon had begun again, the High Council of Time Lords sent at least one investigator, who died quickly without finding out any information. Borusa made the first, second, third and fifth incarnations of the Doctor play the Game. (When Borusa tried to time scoop the Doctor's fourth incarnation and Romana II, he found himself unable to do so because of a time eddy.)
He also transported Susan Foreman, the Brigadier and Sarah Jane Smith there, while Turlough and Tegan Jovanka remained with the Doctor's fifth incarnation in the TARDIS. Together, as Borusa had planned all along, they braved the Death Zone and managed to find the Tomb of Rassilon safely. Meanwhile, the High Council of Time Lords had recruited the Tremas Master to retrieve the Doctor safely out of the Death Zone.
As opponents, Borusa time scooped a Dalek, several squadrons of Cybermen (who unsuccessfully attempted to stage an invasion of Gallifrey), a Raston Warrior Robot and a Yeti.
Ultimately, Borusa hoped to use the enemies to misdirect the Doctors for his real purpose of securing the Tomb of Rassilon, which he believed held the secret of immortality. (TV: The Five Doctors [+]Loading...["The Five Doctors (TV story)","The Five Doctors"])
Following the disappearance of Borusa, Andred led a clean up of the Death Zone with K9 Mark I in order to dispose of what creatures remained there. Also participating was Leela, who personally terminated the Raston Warrior Robot. (AUDIO: Time in Office [+]Loading...["Time in Office (audio story)","Time in Office"])
Seven incarnations of the renegade Time Lord, Iris Wildthyme, along with their respective companions, once encountered a variety of foes including Ice Warriors, Ogrons, Sea Devils, Mechanoids, Zarbi and Quarks as part of a plan by Morbius to gain Rassilon's gift of immortality. (PROSE: The Scarlet Empress [+]Loading...["The Scarlet Empress (novel)","The Scarlet Empress"]) Paul Magrs later wrote that he knew that it had been the Edith Sitwell incarnation of Iris that had called upon the other Irises. (PROSE: Bafflement and Devotion [+]Loading...["Bafflement and Devotion (short story)","Bafflement and Devotion"])
Rassilon created a copy of the Death Zone in his personal sector of the Matrix. This version differed somewhat from the original, with fewer and different snres in place. (AUDIO: Zagreus [+]Loading...["Zagreus (audio story)","Zagreus"])
When Rassilon was resurrected to lead the Time Lords in the Last Great Time War, he turned Borusa into a possibility engine that could see different times and possibilities and often asked his advice. He kept Borusa in his tomb due to how hideous the Time Lord High Council found this. His earlier experiments were left in the Death Zone.
The War Doctor and Cinder entered the Death Zone so the Doctor could see Borusa, but he was unable to transport himself closer. They encountered a lizard-like creature from Gallifrey's past and a large monster which chased them but they escaped into a cliff where they encountered some of the Time Lords Rassilon had experimented on. (PROSE: Engines of War [+]Loading...["Engines of War (novel)","Engines of War"])
The Ninth Doctor claimed he couldn't remember the Death Zone incident when the Brigadier tried to remind him. (AUDIO: Way of the Burryman [+]Loading...["Way of the Burryman (audio story)","Way of the Burryman"])
After the Death Zone's deactivation, Caratessi Thochoser used it as a venue for hunting clones of herself. (PROSE: Tempered [+]Loading...["Tempered (short story)","Tempered"])
Legacy
When the Flux jumbled a number of words from the Thirteenth Doctor's memories, "Death Zone" was among them, being scrambled into "Dozen Heat". The clue written by the Doctor to help readers of her book decode the anagram was "dangerous games". (GAME: Flux Fixers [+]Loading...["Flux Fixers (game)"])
Physical environment
The Death Zone was more than 6,000 square kilometres in size. (PROSE: Tempered [+]Loading...["Tempered (short story)","Tempered"]) Its terrain included mountains, marshes, and at least one paved road. The fog was often so thick that one couldn't see where one was going, and red thunderbolts which would kill instantly frequently fell from the sky, (TV: The Five Doctors [+]Loading...["The Five Doctors (TV story)","The Five Doctors"]) hurled from within the Matrix by the wrathful mind of Rassilon. (PROSE: The Legacy of Gallifrey [+]Loading...["The Legacy of Gallifrey (short story)"]) The Zone was about the size of North Wales, despite those on Gallifrey believing it to cover a great distance. Both Iris Wildthyme and the Doctor knew this. (PROSE: The Scarlet Empress [+]Loading...["The Scarlet Empress (novel)","The Scarlet Empress"]) The Second Doctor described it as "the perfect battle ground". (TV: The Five Doctors [+]Loading...["The Five Doctors (TV story)","The Five Doctors"])
It was inhabitated by animals, often dangerous, from different time zones. (PROSE: Engines of War [+]Loading...["Engines of War (novel)","Engines of War"]) Even after it had been deactivated for centuries, anarchitects still resided in the plain, Eating Fog in the mountains, and nanites in the pools of water. It also contained Sontarans and a gorgaraptix. (PROSE: Tempered [+]Loading...["Tempered (short story)","Tempered"])
Alternative "pieces of the board" to the Death Zone existed and could be exchanged with each other. The sections that were not in use were held in a pocket dimension from which the players could not escape. (AUDIO: The Five Companions [+]Loading...["The Five Companions (audio story)","The Five Companions"]) The entire Zone existed within a time bubble. (PROSE: Engines of War [+]Loading...["Engines of War (novel)","Engines of War"])