Bifröst

One stripe of it is on fire. Before the colours, before the craftsmanship, before the daily traffic of gods and horses, that is the detail the old accounts keep returning to: the red in the arc is not pigment and not refracted light, it is flame, and it is burning for a reason.

A man called Gangleri once walked a long way to ask how you get from earth to heaven. The god who answered him laughed out loud before he spoke, because the question seemed to him about as difficult as asking where the sea is. Had nobody told him the gods built a bridge for it? He had seen the thing already. He probably called it the rainbow. It has three colours, it is very strong, and it was made with more cunning and more magic than anything else the gods have ever put their hands to. That is the whole of the description, and it is worth noticing how little of it is visual. Snorri is more interested in the engineering than in the spectacle.

The bridge carries two names in the surviving poems and neither of them means anything as simple as rainbow. The Prose Edda calls it Bifröst. The Poetic Edda calls it Bilröst, and Rudolf Simek argues that Bilröst is the older form and that it means something like the fleetingly glimpsed rainbow, the road that is gone by the time you have looked twice. Andy Orchard reads the first element of Bifröst as a word for shimmering and gets the shimmering path. Both readings agree on the important thing, which is that the name describes a road that will not hold still. A third name, Ásbrú, drops the poetry altogether and just says whose bridge it is.

Every morning the Æsir ride up it. The third root of the world-ash stands in heaven, and beneath that root is the well of Urd, and the gods hold their court there daily, so the crossing is not a rare and shining event but a commute. Snorri names the horses in order, the way a groom would: Sleipnir first because Sleipnir is best, then Gladr, Gyllir, Glenr, Skeidbrimir, Silfrintoppr, Sinir, Gisl, Falhófnir, Gulltoppr and Léttfeti. One horse is missing from that list and Snorri says why in a half-line, without comment. Baldr’s horse was burned with him.

Thor does not ride. He goes on foot, and he goes the long way, wading four rivers called Körmt and Örmt and the two Kerlaugar, every day, while the rest of them go over his head. The poem gives the reason in a single line that reads like a shrug: the Æsir’s bridge burns all with flame, and the holy waters howl. Picture the strongest of them up to his thighs in cold seething water, taking the ford because the road is too hot for him, and the shape of the whole thing becomes clear. This bridge does not serve everyone. That is the point of it.

At the far end, where the span meets heaven, there is a hall called Himinbjörg and a watchman in it. Heimdallr has gold teeth and a gold-maned horse, needs less sleep than a bird, sees a hundred leagues by night as well as by day, and can hear grass growing in the ground and wool growing on a sheep’s back. He is there for one job. He sits at heaven’s end to keep the hill-giants off the bridge, and when he needs to be heard he has a horn whose note carries through all the worlds. Asked outright whether fire burns over Bifröst, the god answering says yes, and says what it is for in the same breath: that red you see in the bow is burning fire, and the hill-giants would go up to heaven if the crossing were open to all who wanted to cross.

It still will not be enough. The oldest layer of the story is not about a bridge that holds, it is about a bridge that gives way. In the Poetic Edda the dying dragon Fáfnir tells Sigurd where the last battle will be fought, on an island called Óskópnir where the gods and Surt will mix sword-sweat, and then adds the detail that has haunted the myth ever since: Bilröst breaks when they cross it, and the horses swim in the flood. Snorri says the same in plainer words. Strong as it is, it must break when the sons of Múspell ride out harrying, and they will swim their horses over the great rivers and come on anyway.

Gangleri, being a reasonable man, objects. If the gods could build it however they liked, why did they build something that breaks? The answer he gets is the best line in the passage and does not try to defend the workmanship at all. Bifröst is a good bridge. But nothing in this world is of such a nature that it can be relied on when the sons of Múspell go harrying.

What the bridge does, then, is narrow. It joins two places that are otherwise unjoinable and it lets exactly the right traffic across, which is a kind of power the Norse material rarely bothers to dress up. Its limits are equally plain. It burns, so the god of ordinary strength has to ford rivers instead. It is watched, so nothing climbs it unnoticed. And it fails, once, at the only moment its failure matters, under the weight of the one army it was built to keep out. The gods knew that when they made it.

Whether the Norse were looking at anything real when they described it is still argued. Nothing in the surviving Viking-Age record names the bridge at all; the earliest texts that do are thirteenth-century, though Snorri quotes a tenth-century skald, Úlfr Uggason, who calls it the powers’ way. John Lindow and Simek have both raised the Milky Way, which arcs and shimmers but is not red and does not look like it is burning. Rainbows are red only in one band of seven and appear in waterfall spray as readily as in the sky, which makes them poor candidates for a road with a fixed address. In 2024 Christopher Matthew, writing in the European Journal of Science and Theology, put the case for the aurora borealis instead, on the grounds that it is cosmological, arced, flickering, and in the weaker solar conditions of the Viking Age would most often have burned red. The argument is not settled and probably cannot be. What survives either way is a road built out of light by people who assumed that anything beautiful enough to reach heaven would also be too hot to walk on.

Frequently Asked Questions

What is Bifröst in Norse mythology?

Bifröst is the bridge the gods built from earth to heaven. It has three colours and is described as stronger and more skilfully made than any other work of the gods, and one of its bands is burning fire. Snorri Sturluson tells his readers they have seen it already and probably call it the rainbow.

Who guards Bifröst?

Heimdallr guards it. He lives in a hall called Himinbjörg at the heavenly end of the bridge and sits there to keep the hill-giants from crossing, helped by senses sharp enough to see a hundred leagues in the dark and hear wool growing on a sheep. He carries a horn whose blast is heard in every world.

Why does Thor not cross Bifröst?

Because the bridge burns. Grímnismál says that the Æsir’s bridge burns all with flame, and that Thor therefore wades four rivers, Körmt, Örmt and the two Kerlaugar, on his way to the gods’ daily court at the world-ash, while the other Æsir ride over Bifröst on horseback.

Does Bifröst break at Ragnarök?

Yes, and both Eddas say so. Fáfnismál has the dying dragon tell Sigurd that Bilröst breaks when the combatants cross it and their horses swim the flood, and Snorri writes that the bridge must break when the sons of Múspell ride out harrying. Asked why the gods built something that could fail, Snorri’s answer is that nothing in this world can be relied on when the sons of Múspell go harrying.

Is Bifröst actually a rainbow?

Snorri identifies it with the rainbow, but scholars disagree about what, if anything, was originally being described. The Milky Way has been proposed by John Lindow and Rudolf Simek, and in 2024 Christopher Matthew argued for the aurora borealis, pointing out that the texts describe a burning, flickering, red-dominated arc, which fits the northern lights better than either a rainbow or the galaxy.

Related Entries

Heimdallr, Yggdrasil, Urd, Norns, Æsir, Odin, Thor, Sleipnir, Ragnarök, Surtr, Bergrisar, Hrímþurs, Jötunn, Fafnir, Sigurd