Arcopolis
Arcopolis was the name of a large city on a planet which was probably also called Arcopolis. The city was technologically advanced and was the home of a race of near-Human people who had six fingers on each hand.
The city of Arcopolis was devastated by the sudden materialisation of the Fortress, a superweapon capable of destroying all trace of an opponent. Most of the population perished, and "blast shadows" of them were left behind as ghosts which pulled whatever they touched out of reality. The survivors set up a village similar to a Hooverville, and refused to use the technology and resources available in the city on the grounds that it would eventually run out and they needed to learn to sustain themselves. They allowed their children, born after the event, to venture into the city to realise why they must stay in the village.
Fifteen years after the event, the Doctor arrived with the intention of destroying the weapon. The Eyeless detected his TARDIS and arrived before him. The Doctor eventually succeeded in destroying the weapon and defeating the Eyeless.
Twenty years after that, the survivors had a more open view of the city. (TDA: The Eyeless)
