Arcopolis was the name of a large city on a planet in Galaxy Seven. The city was technologically advanced and was the home of a race of humanoids.
The city was devastated by the sudden materialisation of the Fortress in 291,994, which contained a superweapon capable of destroying all traces of an opponent. Most of the population perished, and their blast shadows 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, fearing 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 understand why they must stay in the village.
Fifteen years after the event, the Tenth Doctor arrived with the intention of destroying the weapon. The Eyeless detected his TARDIS and arrived first. The Doctor destroyed the weapon and defeated the Eyeless.