there are several fortresses mentioned throughout the book. the one this one refers to is the one sourounding the great dragon temple in warfang. it is the final defense for the great temple if the walls of the city are breached. the walls of the city's fortress are honeycombed by the elite apartments. these buildings are the only weak point in the structure, but also serve as a rally point for the city's defenders.
The fortress of the city first saw action in the year 2155, when the city was first besieged by Malefor; it was the last refuge for the citizens of the city, being built on a carved platform higher up the mountain then the other districts of the city. It is in the first novelization of the fortress itself being besieged, that the fortress' only weakness, the Elite Apartments, are attacked by the Golem of the Deep, whose aim was to destroy the Upper city, which was considered to be encompassed by the fortress' walls (which subdivided the entire city). the Golem is defeated by the combined efforts of the High Council, Spiril, and Cynder.
During the forth siege of the city, Malefor again uses the Golem of the Deep to attack the city, after failing to storm the gates leading into the Lower district's market plaza, even though walls nearby are breached, and many buildings either damaged or detroyed (including one owned by Hunter). the fortress is only besieged by the Golem; the enemy army never making it into the city thinks to warriors from the Cheetah Tribe.