Anchoring of the thread

The anchoring of the thread was the name given by The Book of the War to the process through which the Great Houses created history with themselves at the centre and, by one account, accidentally unleashed the Yssgaroth. (PROSE: The Book of the War) Another account concurred that Rassilon had "anchored" the Space-Time Vortex using the Eye of Harmony. (AUDIO: Neverland)

The Seventh Doctor described this as Rassilon's decision to make the universe rational; (PROSE: So Vile a Sin) with the Other's help, he thus "shut the door" on the Time of Chaos (PROSE: Lungbarrow) or "Dark Times". (TV: The Infinite Quest, Once, Upon Time)

Ending the "time before this" (PROSE: Christmas on a Rational Planet, The Quantum Archangel) by establishing history using the Eye, (AUDIO: Neverland) the process of rationalizing the universe was a reflection of the Intuitive Revelation (PROSE: Christmas on a Rational Planet) and was synonymous with the Time Wars. (PROSE: So Vile a Sin, The Infinity Doctors) The Founding Conflict which involved the Fugitive Doctor also played a significant role in ending the Dark Times by establishing Time Lord-influenced harnessing of history. (TV: Once, Upon Time)

Before the anchoring
Before the anchoring of the thread, the universe was unstructured and chaotic (PROSE: The Book of the War) in a period remembered as "the time before this" once rationality was established. There were no laws of physics, only infinite possibility, (PROSE: Christmas on a Rational Planet) and "time ran wild". (TV: War of the Sontarans) Astrolabus, an ancient Time Lord who would become one of the first to map the meridians of time, would later deride logic itself as "a new toy" from his perspective. (COMIC: Voyager)

The time before the laying of the thread was variously called the Dvapara Yuga, (PROSE: Dharmayuddha) Dark Times (TV: Once, Upon Time) or Time of Chaos, (TV: The Infinite Quest, PROSE: Lungbarrow) although the latter term was sometimes applied to a narrower period within Gallifreyan history. (PROSE: Cat's Cradle: Time's Crucible) Magick and science coexisted in the universe, although magick predominated. (PROSE: So Vile a Sin) Humanity had divine powers: for instance, Arjuna had one thousand arms and was ardently skilled at compressing time, while Nakula and Sahadeva led armies of imaginary hybrid animals made of broken time. (PROSE: Dharmayuddha)

Devising
Early Time Lord pioneers, such as the Doctor who married Patience, used prototype TARDISes to explore deep time. They returned with "travellers' tales" of "monsters", (PROSE: Cold Fusion, The Book of the War) leading the Great Houses to come to fear that the future would solidify without them: as new cultures emerged and began to impose their own understandings and versions of meaning onto the continuum, a definite framework would emerge. Since these other species could be completely different to the Houses, their assembled history might be inhospitable to the Houses' civilisation; indeed, some members of the Houses had already glimpsed unclassifiable events in the formative future. The earliest time technologies were developed and used to avert such events. (PROSE: The Book of the War)

When Omega, the Other, and Rassilon finished the Hand of Omega, Omega declared that their people could use it to become the Lords of Time and impose their own order upon time. The Other decreed that they had no right to take such an action, reminding his two fellow founders about their failings with the Minyans, yet Omega continued to proclaim the hand was a magnificent development for their people, with Rassilon then agreeing despite his initial concerns about whether they deserved power over time. (PROSE: Remembrance of the Daleks) By other accounts, Rassilon never was cautious about such prospects. (AUDIO: Omega, et. al)

Indeed, it was Rassilon who decided to make the universe rational to end the chaos present in it. (PROSE: So Vile a Sin) To achieve this, the Houses created a causal structure for the future: (PROSE: The Book of the War) the "Web of Time". (TV: Attack of the Cybermen, et. al)

Preparations and machinery
The gods' plan for ending the Dvapara Yuga and beginning the Kaliyuga involved a war between the Pandavas and the Kauravas; specifically, it required Krishna to be killed by an archer. King Jarasandha foresaw this and tried to ensure Krishna would die of old age, but the gods intervened and history was successfully rewritten. (PROSE: Dharmayuddha)

The machinery needed to build the structure of time was bigger than anything else ever built on the Homeworld; (PROSE: The Book of the War) the planetary mass of an engineered planet, dubbed Time, was employed to bind Time, converging in the Temple of Atropos where "all of time" would pass through the six Mouri, whose wills would keep it controlled. (TV: War of the Sontarans, Once, Upon Time)

Proto-timeships embedded themselves at various "strategic points" of space-time, serving to anchor the threads of history into one whole, with these points later becoming load-bearing "node points" of linear history. (PROSE: The Book of the War)

The Eye of Harmony played an important role in the "anchoring" as the "hitching post of chronology", with later legend claiming that the Web of Time could not exist until Rassilon built the Eye. With the Eye active, Rassilon was able to make the universe into one of positive-time, with Gallifrey "anchoring the continuity of the universe" into a system where time was finite. Some academics then pondered if, by the same logic that matter had a counterpart in anti-matter, positive time had a counterpart in the form of a chaotic force called "anti-time". Romana II once stated "positive time, the Web of Time, must have its shadow" according to all the laws (AUDIO: Neverland) of the rational universe Rassilon had established. (PROSE: So Vile a Sin)

According to some obscure legends, the Great Houses preserved a small sliver of irrational reality, the 2nd Second, so that they could reverse the anchoring if it did not go as planned. (PROSE: Weapons Grade Snake Oil) A fragment of a pre-anchoring Earth city survived in an alter-time realm. (PROSE: Cobweb and Ivory) The gods' plan for ending the Dvapara Yuga and beginning the Kaliyuga involved a war between the Pandavas and the Kauravas; specifically, it required Krishna to be killed by an archer. King Jarasandha foresaw this and tried to ensure Krishna would die of old age, but the gods intervened and history was successfully rewritten. (PROSE: Dharmayuddha)

The day
On Gallifreyan Year 0, (COMIC: The Final Chapter) a ceremony was held at the machine-heart on the Homeworld, during which the anchoring was finalised as the structure of history was literally "locked in" (PROSE: The Book of the War) as Rassilon used the Great Key of Rassilon to activate the Eye of Harmony. Standing by his side were a small number of other Gallifreyans, (COMIC: The Final Chapter) elite representatives of the six ruling Houses, there to bond their Houses' biologies with the new structure universe at a fundamental level. At the same time, field agents took their places inside the proto-timeships which had embedded themselves at the future node points of history.

The day ended in disaster as a monstrous entity from outside the universe took this opportunity to break into the space-time continuum, killing most of the representatives and wrecking the machinery. This created the caldera in its modern form. (PROSE: The Book of the War)

Opposition
Some within the reordered universe opposed the Time Lords' decision to bind Time in the service of Space. The Ravagers, two powerful beings, were at the forefront of a war to unmake what the Gallifreyans had wrought and prevent the Dark Times from ending. During the final battle of the conflict, they took control of the Temple of Atropos and banished its six Mouri. However, an elite team of the Division, led by the Fugitive Doctor, was able to capture the two Ravagers and smuggle six Mouri back into the Temple where they once again took their places and controlled Time. (TV: Once, Upon Time)

The Mammoths, who possessed powerful magic and ruled humans on Earth in their original, sentient forms, also opposed the Great Houses' actions. The mammoths on Earth lost most of their powers in the anchoring, preventing them from immediately fighting back. However, their leader Cernunnos survived and would later set about unraveling the Spiral Politic, with one account implying it was he who became the Enemy and sparked the War in Heaven. (PROSE: Cobweb and Ivory)

Consequences for the Great Houses
After the anchoring, the Homeworld was set apart from the rest of the universe as an observer and definer of the Spiral Politic. The Houses' protocols, such as linearity, became laws of physics itself. (PROSE: The Book of the War) The universe's infinite possibility was limited, the Watchmakers instead defining what was rational. This caused whole civilisations to disappear, (PROSE: Christmas on a Rational Planet) as Rassilon now had the power to choose what species developed; he exercised this in his imprisonment of the Divergence, who he saw as a possible rival to the Time Lords. (AUDIO: Zagreus) The imposition of the Web of Time also drove the children of Pythia to powerlessness. (PROSE: Cat's Cradle: Time's Crucible, The Pit, Christmas on a Rational Planet)

However, in doing this, the Watchmakers surrendered the creative and changeable parts of their souls, which collected into a cloud in Gallifrey's atmosphere before being banished into the Time Vortex by the first King of the Majestic Clockwork. (PROSE: Christmas on a Rational Planet)

At the same time, (PROSE: The Book of the War) the Time Lords lost their fertility, prompting the creation of the Looms and the Great Houses of Gallifrey to stabilise the population. (PROSE: Cat's Cradle: Time's Crucible) As a result, the Homeworld began ten million years of total cultural stasis. (PROSE: Unnatural History, The Book of the War) In exchange, they were indestructible, with their meta-structure of history preventing the creation of rival biological forms. (PROSE: The Book of the War)

After-effects
In the wake of the anchoring, multiple parties fled the Homeworld in the First Diaspora. These included the Eremites (PROSE: The Book of the War) and the children of Pythia. (PROSE: Christmas on a Rational Planet) Many notable Great Houses from before the anchoring, like Catherion and Ixion, went into a slow decay that would last millions of years.

According to The Book of the War, on the day of the anchoring, the Yssgaroth escaped into the universe, destroying the site of the machinery and creating the caldera. (PROSE: The Book of the War) This began the Eternal War. (PROSE: The Pit) However, other accounts indicted the Great Vampires were already active in the universe before the Gallifreyans had power over time, (COMIC: Monstrous Beauty) with it also being possible they had escaped into N-Space during Rassilon's early experiments involving black holes. (PROSE: The Pit, Interference - Book Two)

Following the anchoring, magick was banished from the universe. Psi was the last magick that survived, hidden in various cracks and bubbles throughout the universe, because it was the closest to science. (PROSE: So Vile a Sin)

Behind the scenes

 * In the real world, the laying of "anchor thread" is the first step in the construction of a spider web.
 * The Eremites called the Great Houses' founder "Urizen", a reference to the in . In Blake's famous design, Urizen is portrayed as a bearded old man simultaneously creating and constraining the universe with a compass. Urizen's enemy is , the embodiment of imagination.
 * In PROSE: The Infinity Doctors, Lance Parkin equates the anchoring described in PROSE: Christmas on a Rational Planet with the Time Wars period first defined in PROSE: Sky Pirates!. While The Book of the War later indicated that the anchoring took place on a single day, Parkin continued to equate the two in AHistory. In Jacob Black's story for the charity publication Unbound: Adventures in Time and Space, the temporal state of the Time Wars is mentioned to have made them last only an instant.
 * The concept of 'anchoring the thread' to control time is seemingly the Doctor Who franchise's sci-fi answer to the real physics question of 'why the arrow of time only goes forward'.