Archetryx was a planet with temporal shields (powered by gravity wells) which kept the planet a minute ahead of the rest of the universe. It was located in the same system as Etra Prime. (AUDIO: The Apocalypse Element)
The Morestran Orthodox Church was based on Archetryx. (PROSE: Zeta Major)
Archetryx was host to the treaty attended by twenty of the Temporal Powers. At the time, the Daleks returned Etra Prime to the universe on a collison course with Archetryx. The planet suffered extreme damage, but there were survivors. Romana II, Lady President of Gallifrey, promised the Sixth Doctor that she would aid the planet in it's recovery. (AUDIO: The Apocalypse Element)
A convention was held on Archetryx to settle a dispute between the Unvoss and the Nekkistani. (AUDIO: Enemy Lines)