A hive world defined by debate and doctrine, Archaos is divided among five great Collegums, whose rival philosophies of the Emperor and truth itself fuel endless Disputationes Aeternae. Novices compete in brutal examinations: the most gifted ascend to positions of prestige, the greatest become speechwriters for the High Lords of Terra, the failed are consigned to the Munitorum’s bureaucracy—and those who stray too far find themselves in the penal mines, condemned for forbidden thought. Nights in the capital are violent, with gangs of rival novices and cast-off thinkers battling in the streets when words no longer suffice. Despite tainted air and limited resources, Archaos provides manpower for the Imperium, while a Philosopher King nominally rules under Ecclesiarchal oversight.
Ignis Aeternus WH 40K campaign notes 