Great City
The Great City (PROSE: Doctor Who and the Keys of Marinus) was a large pyramid-shaped structure on Marinus. Located on an island in a sea of acid, it was the location of a supercomputer, the Conscience of Marinus, which had Arbitan as its custodian.
The city was visited by the First Doctor, Susan, Barbara and Ian when shortly after they first arrived on Marinus. There, they encountered Arbitan, who coerced them into finding the three microcircuits, or "keys" to the Conscience to help him defend the planet against a Voord invasion. (TV: "The Sea of Death") After finding the keys across Marinus, the four returned to the city to find Arbitan dead and Yartek in control of the city. The Voord were killed when a false key was inserted into the machine, destroying it. (TV: "The Keys of Marinus")
