Barrier spells

Barrier spells (or Containment spells) are spells which appear as Latin phrases or inscriptions. Ghosts cannot cross barrier spells, as they must obey whatever the spell says, according to what Dennis Rafkin explained about the supernatural realm having its own set of rules to follow. While some barrier spells are always visible, the "hidden" barrier spells can only be seen through spectral viewers. Barrier spells can be used either to contain ghosts or as a shield against them.

Cyrus Kriticos had the glass walls that made up Basileus's Machine etched with barrier spells in order to prevent the ghosts needed to power the machine from escaping.

Trivia

 * At least one of the spells is the Lord's Prayer in Latin.
 * According to Dennis Rafkin, the spells used against the ghosts can either be written or spoken.
 * Based on what Dennis Rafkin suspected, Cyrus installed hidden barrier spells to ensure more protection against the ghosts.