When it was an Imperial world, it was controlled by a race of Crocodilians. When those they oppressed overthrew them, it resulted in the decimation of the planet. A few of the royalty managed to escape before that happened. They took the Skull of Sobek with them, which was a data repository of the history of the planet.
The skull eventually was moved to Indigo 3, where it was incorporated into the framework of the New Hall of the Sanctuary of Imperfect Symmetry. When the Eighth Doctor and Lucie Miller visited the Sanctuary, the culture of Sobek was ten thousand years old. (AUDIO: The Skull of Sobek)