Most states have prisons, our prison has a state...

[Samael Morgenst]

Mh, the idea was about ruling a prisoner population, not merely confining it.

Those are some ideas I had:

* Mark of Justice (Clr 5): has no xp cost or material component, and has permanent duration: one for each prisoner, with the activating behavior being: "disobey the prison rules in any way, by action or inaction", with the prison rules basically demanding unconditional obedience.

* Geas (Clr 6): no xp/material cost, duration is indefinite if the task is not open ended; it's enough to establish a very time consuming task (some variation of "serve the prison director's untill you have produced at least a million gp of raw wealth").

* Hypnotism (Wiz/Sor 1): not true mind control but can implant a single permanent suggestion and at least ameliorate the prisoners attitude. Somewhat. Every little bit helps.

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About the location, I was thinking about a subterranean complex, shaped into raw rock and soil through multiple Stone Shape and Wall of Stone spells. Either subterranean race as prisoners (orcs and half orcs), or bioluminescent fungi for illumination (and subterranean farming).