From either edge of Nifl-heim, arching high above Midgard, rose the sacred bridge, Bifröst (Asabru, the rainbow), built of fire, water, and air, whose quivering and changing hues it retained, and over which the gods travelled to and fro to the earth or to the Urdar well, at the foot of the ash Yggdrasil, where they daily assembled in council.
“The gods arose
And took their horses, and set forth to ride
O’er the bridge Bifrost, where is Heimdall’s watch,
To the ash Igdrasil, and Ida’s plain.
Thor came on foot, the rest on horseback rode.”
Balder Dead (Matthew Arnold).
Of all the gods Thor only, the god of thunder, never passed over the bridge, for fear lest his heavy tread or the heat of his lightnings would destroy it. The god Heimdall kept watch and ward there night and day. He was armed with a trenchant sword, and carried a trumpet called Giallar-horn, upon which he generally blew a soft note to announce the coming or going of the gods, but upon which a terrible blast would be sounded when Ragnarok should come, and the frost-giants and Surtr combined to destroy the world.
“Surt from the south comes
With flickering flame;