Arkhaven was a city on Sarath. It was governed by Brantus Draad through the artificial intelligence called Monitor. Although Arkhaven was not the capital city of Sarath, it soon became the last hope for the planet's human population after Sarath's moon was struck by an asteroid and sent into a descending orbit towards the planet. Even when it appeared that most other cities and civilisations on Sarath had been destroyed, including their capital city, Arkhaven remained reasonably intact, as it was mostly self-sufficient and able to supply itself with food and power, while its location in a relatively geologically stable region meant that it only had to deal with the threat of relatively predictable meteor bombardments.
Faced with the destruction of their planet, the citizens of Arkhaven began work on a ship that would take survivors to the neighbouring planet Mirath. A war with the Taklarians decimated most of Arkhaven's population, leaving only around eighty thousand alive when the city had originally had a population of over five million, but the government covered up the scale of the deaths using hollowed illuminated buildings and various automatons to give the illusion that the population was much higher. In order to maintain control, the word was put out that the Ship was already at maximum capacity, thus allowing them to send any surviving refugees or citizens objecting to the current policies to the NC2 - Non-Citizen, Non-Conformist - camps, with NC2s scheduled to be left behind when the Ship departed.
In reality, the Ship was a deception as Arkhaven didn't have the power to create a working model of a ship that size, with the actual evacuation craft being the Ship's Lunar Lander, capable of only holding around five hundred people who were carefully chosen by those aware of the situation. The majority of Arkhaven's population were sedated and left on the Ship before it was destroyed, but various NC2s and others were led to the Lander by the Doctor and his companions when an attack by the surviving Taklarians delayed their opportunity to board the original Ship. With Arkhaven now holding less than half the required population of at least 1000 to exist as a legal entity, Monitor attempted to stage a coup, knowing that the current society would be unable to maintain the level of technology necessary to continue his existence. Fortunately, after Monitor was destroyed, the Lander departed using a "portion of folded space" from the TARDIS to give it extra internal space for the NC2s. (PROSE: City at World's End)