Anarchitects were conceptual entities created by the Celestis using flux technology (PROSE: The Book of the War) and used as weapons by the enemy during the War in Heaven.
The anarchitects were disembodied intelligences which were able to inhabit architecture and disrupt the information that held it together, allowing them to rebuild entire cities at will. This technology was the same that the Time Lords had used by the early TARDIS models, but they'd never thought to use it as a weapon of war. (PROSE: Alien Bodies) One anarchitect was capable of "possessing" a single structure, regardless of size.
However, the "rewriting" of physical structures was achieved by manipulating the meaning of these structures rather than the matter. Like other conceptual entities, the anarchitects lacked physical form and only existed in the mind of the beholder, which they would manipulate to warp that person's understanding of their relationship to their world-environment.
Bridges can disappear underfoot, simple corridors can become impenetrable labyrinths, while spaces can become oppressively small or horrifyingly large without warning. And yet the anarchitects achieve this without actually changing the substance of the building at all.
As a result, because they were purely non-physical, anarchitects could not be combatted by casts. Time-aware posthuman species attributed the effects of anarchitects to nanites.
A flaw in the early anarchitect program was a well-developed sense of self which could lead to conflict with the anarchitect's user. This flaw particularly pronounced in the gargoyles, a previous iteration of the technology. (PROSE: The Book of the War) The shifts were later created by applying the same principles to living subjects. (PROSE: Alien Bodies)
Instances[]
Homunculette faced an anarchitect in the ruins of London after the 22nd century Dalek invasion: a bridge disappeared right from under his feet, and he fell into the polluted River Thames. When he told this to Marie, she asked him if he was sure he didn't just fall off. (PROSE: Alien Bodies)
The Remote had anarchitect-derived weaponry in their weaponstores, but they rarely used it on the battlefield. Some Remote left a "ship-killer anarchitect" behind as they left the Venue Accords, but it remained dormant. (PROSE: The Book of the War)
According to a rumour, Lord Ruthventracolixabaxil starved to death in his own TARDIS when an anarchitect hijacked it and turned the central corridor into an endless Möbius loop. (PROSE: Alien Bodies) In reality, he had been consumed by Lolita. (AUDIO: The Shadow Play)
Some theorists suggested that anarchitect techniques were used in the creation of the City of the Saved. (PROSE: The Book of the War)
Even after the Death Zone on Gallifrey had been deactivated for centuries, anarchitects still lived in its grassy plain. When Caratessi Thochoser visited, they had just finished feasting on Sontarans. (PROSE: Tempered)