In "The Last Olympian" by Rick Riordan, the author uses vivid imagery to describe the overwhelming sound of an approaching army. The comparison to a fierce cannon barrage combined with the energetic roar of a packed football stadium captures the intensity and chaos of the moment. This auditory depiction conveys a sense of dread and impending confrontation as the characters prepare to face their adversaries.

The simile effectively illustrates the atmosphere of tension, making readers feel the energy and anxiety in the air. It emphasizes how the characters must brace themselves for an epic battle, heightening the stakes of the narrative while drawing readers deeper into the action of this fantasy world.