Group Hold was a level 7 spell.
All the guards outside had professions above grade 3. Those who could make them feel nothing must have used some unique technique to Instant Cast. Instant Cast Spells required an additional three Spell Levels, which meant that the difficulty of this Instant Cast 'Group Hold' spell was equivalent to a legendary spell. When the middle-aged woman discovered the anomaly, she was immediately sure that they were dealing with a legendary Wizard or Priest.
Some special Priests were also able to cast Group Hold.