Islos

Islos was a planet. It was the home to the Archive of Islos. The planet was defended by orbiting weapons platforms

It was attacked by the Dalek fleet, led by the Emperor of the Restoration, as they were aiming the Archive. The Daleks managed to cause large damage to the planet, but the Archivians surrendered the Archive only when the Emperor threatened to destroy it. The population of the planet escaped through a portal inside the Archive, taking its contents with them. In exchange they offered the Daleks to the race that saved them. (WC: The Archive of Islos) After the Daleks realised that it was a trap they retreated the planet and headed for Skaro. (WC: The Sentinel of the Fifth Galaxy)