The Nine Gallifreys or Nine Homeworlds project involved the cryptoforming of eight planets into eight cloneworlds of Gallifrey. (PROSE: The Shadows of Avalon, The Book of the War) It was originally planned by Greyjan the Sane (PROSE: The Ancestor Cell) and eventually spearheaded by House Mirraflex's Lady Armourer Mantissa and House Lineacrux.
Officially, each Homeworld was run by a caretaker House as a potential replacement if the original Homeworld were destroyed. However, the backup Homeworlds also acted as decoys, with each having its own War King or War Queen and thinking it was the original. There was a supposedly-total ban on contact between Homeworlds, but Mantissa eventually went into exile on one of the duplicates, (PROSE: The Book of the War) and by the time of the fall of Mictlan, travel between Gallifreys was often performed by the War King and his agents. However, even after travel between Gallifreys became common, not even the War King knew which was the original. (PROSE: The Taking of Planet 5)
Since each thought it was the true original, the secondary Homeworlds each created their own tertiary Homeworlds; some House Military strategists hoped this would end in every planet being turned into a Homeworld. (PROSE: The Book of the War) Some Gallifreys were hidden in pocket universes; (PROSE: The Taking of Planet 5) one Great House (AUDIO: The Eleven Day Empire) notably created a homeworld on Christine Summerfield's Earth in the bottle universe. (PROSE: Dead Romance) A human colony-world was cryptoformed by the Great Houses into a Homeworld between 3560 and 3591, and some of its inhabitants like Verrifant were mutated into regen-inf soldiers. (PROSE: The Book of the War)
Six years before the War, the War King became Lord President of what purported to be the original Homeworld, and he continued in that role for over half a century. (PROSE: The Book of the War) When Compassion became the first 102-form timeship two years before the War, (PROSE: The Book of the War) Romana was also War Queen (and "Mistress of the Nine Gallifreys") on what seemed to be the original Gallifrey. (PROSE: The Shadows of Avalon) This Gallifrey was invaded by Faction Paradox and destroyed sometime before the Eleven-Day Empire was destroyed in the War's fiftieth year; (PROSE: The Ancestor Cell, The Shadow Play) at that time, the Faction claimed to have also written the backups out of existence. (PROSE: The Gallifrey Chronicles) The incident where a Gallifrey was first lost was called the battle of Mutter's Cluster. At the time, this brought the "official" total down to nine. (PROSE: The Taking of Planet 5)
Sometime after the wiping of the original Gallifrey, in which most Time Lords perished, Homunculette was taught the basics of escapology by War Cardinals at a training complex on Gallifrey XII. (PROSE: Alien Bodies) Homunculette and the Lord President once visited Gallifrey Eight, which contained loomstacks and chronoforges to create weapons and soldiers for the Time Lords. (PROSE: The Taking of Planet 5)
In her lecture "The Cultural Impact of War-Time", Entarodora noted that more Homeworlds had been lost "than might be thought prudent". She argued that the total number of War-time deaths by Great House members was nonetheless small because the inhabitants of these other Homeworlds were "mere-sheath echoes" of a "core probability". At least one Homeworld was predicted to be destroyed upon the destruction of the Hydra-Centaurus Cluster by the Grandfather's Maw around the year 60,000,000,000. (PROSE: The Brakespeare Voyage)