Tyrael: Yes, but for how long? Our time grows short! We must take this fight to Azmodan!
Necromancer: To the battlefields, then!
Go through the Arreat Gate outside the Bastion's Keep Stronghold
Defending the keep will only get us so far. The time has come to press the attack on the fields themselves, and show Azmodan that he has grievously underestimated us.
Tyrael: Can you feel the keep shuddering? Azmodan's siege weapons. Saving these walls will have meant nothing if they're reduced to rubble.
Necromancer: Indeed. I'll defend them.
Templar: At last!
Note: Go to the Bastion's Keep Stronghold, then leave through the gate to the outdoor.
Go straight. A door is opened -- leading outside of the fortress into The Arreat Gate.
Necromancer: The keep is secure. Our fight continues in the battlefields.
where Azmondan's war machines rain death on our soldiers.
Talk to Sergeant Pale east of the Arreat Gate outside the Bastion's Keep Stronghold
LOCATION: THE ARREAT GATE
Soldier: Do you think she's as good as they say?
Soldier 2: She wouldn't have made it this far otherwise.
Templar: It feels good to be on a battlefield again.
Sergeant Pale: Thank the gods you're here! You've got to destroy those ballistae; they're raining hell down upon us! We can't last much longer!
Cross the Bridge of Korsikk in the Battlefields
Note: Continue moving diagonally in a straight line until you reach the border, then explore to the east until you find a path forward. You might need to go downstairs and go through obstacles. Once you get past the bridge, you will find The Bridge of Korsikk Waypoint.
LOCATION: FIELDS OF SLAUGHTER
You will find the 3 ballistae in the Fields of Slaughter. The mini map shows the ballistae icon when you are closeby.
Destroy the Demonic Ballistae and the Trebuchet Device on the Fields of Slaughter northeast of the Bridge of Korsikk.
Demonic Ballistae destroyed (0/3)
Trebuchet destroyed (0/1)
The Trebuchet is hidden behind this gate.
Templar: By the Light! That must be the trebuchet. Strike now!
Destroy all the Demonic Ballista.
Vision of Azmodan: I do not need my siege weapons to slay you. You stand in the middle of the Army of Hell. It will crush you!
Necromancer: You waste your breath, demon.
Talk to Tyrael at Rakkis Crossing northeast of the Fields of Slaughter
With the war machines felled, it only makes sense to continue onward toward the crater. It is hard to anticipate what I shall see there... The books of the necropolis library only contained vague descriptions of the Burning Hells: realms of smoke and fire and endless peril.
Tyrael: I could no longer sit idly by while you brought the fight to Azmodan. It has been too long since I felt the thrill of battle myself.
Vision of Azmodan: Destroying my siege weapons makes little difference! Every hour, more of my forces pour forth from the mouth of Hell. Soon, they will wipe your pathetic keep from existence.
Tyrael: Brave words, Azmodan! But words are all you have left to hurl at us. Forward, friend! Now we shall drive Azmodan's army back into the accursed crater!