As Arthas ordered the Kirin Tor's surrender, Antonidas came to greet him.
Arthas: Wizards of the Kirin Tor! I am Arthas, first of the Lich King's death knights! I demand that you open your gates and surrender to the might of the Scourge!
Antonidas: Greetings, Prince Arthas. How fares your noble father?
Arthas: Lord Antonidas. There's no need to be snide.
Antonidas: We've prepared for your coming, Arthas. My brethren and I have erected auras that will destroy any undead that pass through them!
Arthas: Your petty magics will not stop me, Antonidas.
Antonidas Pull your troups back, or we will be forced to unleash our full powers against you! Make your choice, death knight. (Antonidas teleports away)
Kel'Thuzad: I sense that three separate wizards are maintaining these auras. If you find and kill them, the auras will disperse.
Arthas entered the city with his army. They killed the first wizard.
Kel'Thuzad: The Archmage has been killed. The first aura is dispersing.
After wich they found cages.
Kel'Thuzad: The Kirin Tor keeps these creatures caged for studying. If they were to be released, they would cause our enemies a great deal of pain.
As they marched further, they encountered the base of the Mage's guild. After the base was destroyed they encountered the second Archmage.
Kel'Thuzad: The second wizard has fallen. Only one cursed aura remains.
As the assault continued Arthas found a vault.
Kel'Thuzad: The wizards keep many enchanted items within that vault. Shatter it, and we can use their own weapons against them.
And then attacked the base of the Sorcerer's league. As they moved on they reached a crossroads: To the north was Antonidas, and to the west was The Kirin Tor's base. Arthas destroys both.
Antonidas: It pains me to even look at you, Arthas.
Arthas: I'll be happy to end your torment old man. I told you that your magics could not stop me. (Arthas kills Antonidas)