This line means, “At the sonorous roar of the cannon.” It completes the chorus by connecting the trembling earth to the sound of artillery. The anthem uses the cannon as a symbol of war, defense, and national strength.

Sonoro means “resounding” or “loud and ringing.” Rugir means “to roar,” a verb often used for animals, storms, or engines, so rugir del cañón gives the cannon an animal-like power. Cañón is “cannon.” Together, the line is not subtle: it is meant to sound loud, martial, and dramatic.