|Joseph William Turner, Interior of a Prison|
Sometimes truly destroying a demon is impossible or impractical. In such cases, magical seals are sometimes employed. Clerics may learn the seal evil rite upon reaching fourth level. Learning requires four months study with a holy text describing the rite or one month of study with a cleric can can perform the rite. Creating a seal is closer to creating a magic item than casting a spell. It requires one day of work (regardless of the seal level) and 100 gold pieces per level of seal. A cleric may not create a seal of level higher than their experience level as a cleric. So, for example, a fifth level cleric could create a fourth level seal at the cost of 1 day of work and 400 GP in expenses. The same cleric could not create a seal of strength higher than fifth level.
However, multiple clerics working together may create stronger seals. All clerics so cooperating must have learned the rite (and thus must be at least fourth level). For each cleric in excess of the first, the strength of the seal is raised by one level, to a maximum level of 20. The time to complete the rite is still one day, but costs are commensurate with the final level of the seal (so a 15th level seal created by a 7th level cleric and eight assistant clerics would take one day and 1500 GP in sacrifices and components).
Seals work by preventing magical or chaotic beings from passing through the warded area, usually a door, though a physical barrier is not required. Such beings include elementals, undead, demons, powerful sorcerers, and cauldron-spawned beastlings (but not natural humanoids or animals, even if dangerous). Affected creatures inside the sealed area with hit dice equal to or less than the level of the seal may not in any way cross the barrier. In addition, if the barrier is an entrance into a closed area (such as a room, coffin, or complex), such creatures may also not leave via any other route (for example, tunnelling through dirt around the door is not possible). In addition, all the benefits of a protection from evil spell are present.
Clerics of any level can immediately identify a seal and ascertain its potency. In addition, clerics of fourth level or higher can read any details included (seal inscriptions are written in the hidden language of law). Magic-users will recognize a seal but must make an intelligence check to determine its level. Seals detect as magical, and read magic can be used to uncover details about the evil being warded against (if the seal creator decided to include such information). Anyone else may identify a seal with a successful intelligence check, though no details about its power or reason for being should be provided. A sage can often assess the level of a seal if provided with rubbings or sketches.
Creatures with more hit dice may attempt a saving throw versus spells once per lunar cycle to break the seal. If successful, the seal is destroyed. In addition, unless accompanied by a cleric who knows the seal evil rite, anyone crossing the threshold will break the seal. Thus, creatures trapped within a sealed chamber will often seek to trick or tempt mortals into transgressing the seal.