Bifrost



The Bifrost Bridge is a transportation device used by the Asgardians. It is guarded by the warrior Heimdall at his Observatory. The Bifrost Bridge is a link between all the Nine Realms, but can be opened only if Heimdall permits it: the bridge is in fact much too powerful, and it would destroy all realms if left opened.

Thor, Loki, Sif and the Warriors Three used the Bifrost to reach Jotunheim, thus reigniting an age old conflict with the jotuns. Loki's machinations behind this affair culminated in an attempt to destroy Jotunheim by leaving the Bifrost open on that realm, but Thor foiled the plan by destroying the Bifrost instead.

With the Bifrost destroyed, the Asgardians became cut off from the worlds that they protected, and the Nine Realms were consequently plunged into chaos.[2] They hastily rebuilt the bridge, which Heimdall then repowered with the Tesseract, and then set forth on a campaign to rid the Nine Realms of the marauders that had grown in strength during their absence.[3] During this time the Bifrost was put to frequent use transporting Asgardian raiding parties to the other realms, and to bring their prisoners back to Asgard

History
Bifrost, known as the Rainbow Bridge was the connection between Asgard and Midgard, the Earth. It was guarded by Heimdall before it shattered after the events of Ragnarok.