In the Archduchy of Dietsas Pleeprius ruled by a Confederacy, a character must undergo a Trial by combat.
He has been framed by A collusion of guilds - uses resource control for leverage - and if found guilty of Treason, his punishment will be Symbol of Death. Cast Permanency, place the symbol so its 60 foot radius crosses the only entrance. Cast Curse on the prisoner to lower their saving throw. This still gives the prisoner a chance at a saving throw, so you will want to target those with naturally poor Fortitude, and this is better as a deterrent than a cell because the desperate will take their unknown-but-poor chances of surviving, sometimes. Substitute other Symbols to create other defenses in the prison.

Archduchy - The dominion of the archduke, who is higher ranking than the grand duke, but still beneath the king. Usually a member of the royal family in line of succession.
Confederacy - A union of persons, parties, or states; a league.
Trial by combat - Fight to the death, winner is innocent