Rock Flesh

In Necromancy, Rock Flesh is an excellent defensive spell.

Spell Description
With the spell Rock Flesh, the Necromancer turns their skin skin as tough as rock, essentially making the caster temporarily invulnerable to any kind of physical injury. This is an exellent spell to cast before passing a known danger zone, having the same effect as drinking a purple potion. However, unlike said potion, it lasts 100 seconds longer. Also note that it only negates injury damage; heat damage from lava or drowning in water are still very lethal.

Trivia

 * This spell (apart from using a potion) is the only way in the Shrine of the Ancient Ones to pass through the colored beams of death.
 * A purple potion in Ultima VIII does have the same effect as the spell, but since these are rare to find, it generally is better to use this spell instead.