Frontier in time
The frontier in time was the area in the universe's far future past which the Great Houses could not see or safely travel because so many other time-aware cultures are active in the later universe. The frontier appeared as the posterior end of recordable history in the Spiral Politic and obscured the homeworlds of many posthuman cultures.
The enemy patrolled the frontier to time and the areas beyond, suggesting that enemy forces may have been in full operation beyond the frontier. Homeworld timeships were frequently repelled from this region of the Spiral Politic and, more disturbingly, as many as five were destroyed or captured along with their occupants. Compassion found the crumpled remains of the 103-form timeship Percival on the frontier, abandoned on a barren rock on the edge of posthuman history. Percival's pilot was still alive despite having been stripped of all his major organs, though he died after a few hours on the Homeworld. Carmen Yeh told of this event and Compassion's subsequent confrontation of the War King in her fictionalised memorial Fantastical Travels in an Infinite Universe.
Since they preferred to believe themselves to be masters of causality and overseers of the whole continuum, members of the Houses rarely ventured into the frontier. (PROSE: The Book of the War) The Tenth Doctor said that Time Lords never went as far as the year 100,000,000,000,000, though the War Master went there during the Last Great Time War. (TV: Utopia)
When an expeditionary cohort of the Seventh Wave was cut off from Homeworld contact close to the frontier with only an outmoded 89-form timeship, Quintessence Officer Hierarchio predicted their chances of return to be minimal and suggested that they settle on one of the still-accessible worlds. There, the troops visited the Anvil Stars region and observed the birth of new universes and the creation of Leviathans.
A Violent Unknown Event occurred on Zo la Domini at the frontier in time. Thessalia chose a different location on the frontier (PROSE: The Book of the War) to unleash the babel. (PROSE: Newtons Sleep)
The Uptime Gate to the City of the Saved was located in the universe almost exactly on the frontier in time. The Book of the War suggests this may imply detente or even alliance between the City and whatever forces patrol the frontier.
Faction Paradox had links to underworld or terrorist cabals in the posthuman worlds beyond the frontier in time. They had no difficulty crossing the frontier and voyaging into the depths of the posthuman period; though the Houses accused them of conspiring with posthumans who scavenged wrecked Homeworld technoogy, the Faction instead voyaged past the frontier just for the satisfaction of doing something the Houses had made taboo. (PROSE: The Book of the War)
