In Norse mythology’s Ragnarök, Heimdall blows the horn that signals the final battle.
Heimdall is the vigilant guardian of the gods and watches over the rainbow bridge Bifröst. He possesses the Gjallarhorn, whose sound can be heard throughout the worlds. When the enemies of the gods approach, Heimdall blows it to warn the divine community that Ragnarök has begun.
Heimdall’s role as watchman explains why the warning belongs to him rather than Odin or another leading god. The horn is a separate object from the bridge itself, and the horn’s sound is the signal that summons the gods to action.
At Ragnarök, Heimdall and Loki fight one another and kill each other. The warning and the final duel are distinct episodes in the same end-of-the-world sequence.