The Althosian system was a star system with seven planets and two suns. The planets within the system were collectively called the Seven Planets. Six of the seven planets were inhabited; the last "planet" was actually an artificial construction and was not inhabited. Hunters lived around the Althosian system, where they were attracted to the seventh planet.

The seven planets were originally Earth colonies, but they declared independence in 2396. They were all destroyed in 2400.

The planets included Nicaea, Trieste, Byzantine, Cosgon and a large, unnamed planet.

Nicaea, capital of the Althosian system, was governed by the Academy. The Academy was based on the Greek philosophical kings, with the most intelligent people leading the Seven Planets. The Academy was led by the Archon.

Trieste was the home world of the Kython, an oppressed native species.

Cosgon was known to be icy and cold.

One was actually an artificial construction by Kopyion Liall a Mahajetsu to keep the Yssgaroth trapped. (PROSE: The Pit)

Jason and Dr. Who considered the destruction of the Althosian System's seven planets to be one of the Doctor's greatest crimes. (PROSE: Head Games)

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