Deep time

Even before taking control of history, the Great Houses of those who would soon become the Time Lords sent pioneers to explore "deep time", or "deep-time".

Ancient Gallifreyan Patience's husband, seemingly a version of the Doctor before the "First", was "a pioneer and leader among [the Doctor's] people, one of the first Gallifreyans to enter the Time Vortex after it was discovered". He notably "led an expedition into deep time", returning with "travellers' tales of monsters and lost civilisations". (PROSE: Cold Fusion) As recounted in The Book of the War, prior to the anchoring of the thread, "early deep-time explorations performed by the Great Houses' pioneers" showed that there were "things at work in the formative future, things which simply couldn't be classified or even monitored by the Houses' own technology". This contributed to the Great Houses' decision to become lords of history. (PROSE: The Book of the War)