If you ever find yourself facing a wizards' duel, I suggest you run away as fast as you can.— Brom
A wizards' duel was a form of combat that used magic as the primary weapon. It consisted of breaking into an opponent's mind, reading his thoughts, anticipating his actions and then countering the moves. The other must, using magic, block their spell, which was almost impossible without infiltrating the other person's mind. There were strict rules for dueling: breaking the rules resulted in death for both contestants.
Few people could survive a duel for more than a few seconds, as dueling required a great deal of skill and strength. Galbatorix was a master in wizard duels, as he had a keen ability to detect and infiltrate others' minds.