Her munition; i.e. her defenses the walls and towers in which she put her trust (comp. Isaiah 29:3). As a dream of a night vision. "The baseless fabric of a vision," when it has once passed by, "leaves not wrack behind."
The entire host of the "terrible ones" would melt away and disappear, as a night vision before the light of day—it would dissolve into nothing, vanish, leave no trace.