Slay Watchkeeper Gargolmar, Vazruden the Herald and Vazruden's drake, Nazan. Return Gargolmar's Hand and Nazan's Head to Advance Scout Chadwick.
Hellfire Citadel's entire defensive network relies on the ramparts as a sort of early warning system.
You need to take out Watchkeeper Gargolmar and Vazruden the Herald. Without them, taking the ramparts will be simple.