Gjallarhorn

In Norse mythology, Gjallarhorn is the "ringing" horn belonging to Heimdall, the watchman of the gods. Heimdall resided at the entrance to Asgard, guarding the Bifrost bridge, and possessed extraordinary senses, able to see great distances and hear grass grow.1

The Gjallarhorn was believed to be heard throughout all realms. Heimdall would sound it to alert the gods when their enemies, the giants, approached during Ragnarök, the prophesied end of the world. This cataclysmic event involves a final battle between the gods and their adversaries, leading to the death of many gods and the eventual rebirth of the world. Heimdall himself is fated to slay the trickster god Loki during Ragnarök, though both will perish.12