Shield Spell

A shield spell ("Scildan!") is a powerful form of enchantment used by a sorcerer to protect himself. It creates a large half-sphere of magical energy that stops the enemy's attack. It's unknown if this spell can only protect its caster from another magical assault or even form other objects, like arrows.

Merlin used this spell to protect himself from Kilgharrah when the angered dragon breathed fire against him. The young warlock displayed his powerful magic with it, being able to stop completely the Great Dragon's attack (Le Morte d'Arthur).