The Feral World of Iphigenia in the Jericho Reach is, in many ways, typical of the T'au Empire's Velk'Han Sept. It is a Human world with a population of around seven billion, living mostly in the polar cities spared the fierce heat of the planet's nearby red sun.
Its people are all born into one of several dozen tribes, each tribe having its own king in turn united under the "high king." All laws are decided according to the tribe; transgressions in one tribe are often accepted in another, even though the populations of the various tribes live side by side in every city.
Since Iphigenia was absorbed into the sept, however, another power structure has come to exist alongside the tribal kings: the "Grey Kings," the name given to the T'au emissaries who have entered into an agreement with the high king.
In return for allowing the Human tribes to rule themselves, the Grey Kings require Iphigenia's armed forces to fight for the T'au as Gue'vesa. In addition, the tribal kings are to hand over the most technically skilled of their people to the orbital stations on which the Grey Kings live.
Each station is a huge re-education facility. Many of the Gue'la sent here are trained in T'au technology and sent to work elsewhere in the sept under Earth Caste work teams or Air Caste starship crews.
Others are sent back down to Iphigenia, radiant with their new purpose and eager to spread their understanding of the Greater Good among their tribemates.
Iphigenia's people are far from universally convinced about the Greater Good. The "enlightened ones" who return from orbit, however, are quick to address such concerns with anyone who wishes to accompany them to the strange structures the Grey Kings are building in the southern wastes.
- Deathwatch: Core Rulebook (RPG), pg. 353