In Norse mythology, what horn does Heimdallr blow to announce Ragnarök?

In Norse mythology, Heimdallr blows the Gjallarhorn to announce Ragnarök.

Heimdallr is the watchman of the gods and guards the Bifröst, the rainbow bridge connecting Asgard with other worlds. His extraordinary sight and hearing allow him to detect approaching danger, including the forces that gather for Ragnarök.

The Gjallarhorn is also associated with the god Heimdallr in descriptions of the world’s final conflict. Its blast signals the gods and their allies that the battle has begun. The name is often translated as “resounding horn” or “ringing horn.”

A common mix-up is confusing Gjallarhorn with Gungnir, Odin’s spear, or Gram, the sword associated with Sigurd. The horn is an instrument, not a weapon. In some modern retellings, its sound is treated as a general symbol of doom, but the myth specifically links it to Heimdallr and Ragnarök.