Volcanic planet. At one time, it was a Trion colony, but proved to be too inhospitable because of its volcanic activity. While the Trion used it for its regenerating Numismaton Flame, the planet's inhabitants slowly reverted to tribalism and superstition. After the revolution, the Trions used Sarn as a dumping ground for their political prisoners. The Sarns worshipped Logar, god of the Fire Mountain, and sacrificed any Unbelievers. The Fifth Doctor defeated the Master on Sarn. Turlough summoned Trion's help to evacuate the Sarns, who were threatened by a volcanic eruption (6Q).