Madillon Cluster
The Madillon Cluster was a star cluster; Earth, which was twelve days hyperspace travel from the Third Zone, was located between the Zone and Madillon. (PROSE: The Two Doctors) Samur was located in the Madillon Cluster. (AUDIO: Heroes of Sontar)
In the 20th century the Sontarans planned a vital attack in the Cluster, with the Ninth Sontaran Battle Group staged there while Group Marshall Stike attempted to use the Kartz-Reimer module to gain time travel on Earth. (TV: The Two Doctors)
A Sontaran sergeant still alive in 2371 had led troops in the Madillon Cluster before they were all wiped out. (PROSE: Lords of the Storm)
The Madillon Cluster was one of the places the Sixth Doctor speculated as a possible location of dormant Cybermen after the Great Cyber War. (AUDIO: Last of the Cybermen)