Sleep Field

One of the spells to create a magical field is Sleep Field.

Spell Description
Using Sleep Field spell creates a magical sleep field that will cause everyone that comes too close to it to fall asleep. However, its use is rather limited. If not cast on a narrow path, the caster's foes can simply walk around it. It is also important to note that the field dispells itself after several creatures walk into it - at least in newer incarnations, since in older times the field was very much permanent.

The spells Sleep and Mass Sleep are similar spells, but targeted directly at the caster's enemies.

History
Note that Energy Field was originally an umbrella term for all the types of magical fields: Poison Field, Fire Field, Sleep Field and Lightning Field, and the same spell would be used to create any of them. Later (after Ultima IV), different spells were designed for each of the fields, and the previous Lightning Field came to be known simply as Energy Field. However, at times the four spells are still called "energy field spells".