What is the name of the horn vikings sounded for battle?

The horn that Vikings sounded for battle is called a "Gjallarhorn." It was traditionally associated with the Norse god Heimdallr and was used to signal important events, including the start of battles. The Gjallarhorn is often depicted as a large, curved horn made from animal horn or metal. Its sound was believed to rally warriors and instill a sense of urgency during combat.