Myths of the Norsemen From the Eddas and Sagas
Page: 10As the tree Yggdrasil was ever green, its leaves never withering, it served as pasture-ground not only for Odin’s goat Heidrun, which supplied the heavenly mead, the drink of the gods, but also for the stags Dain, Dvalin, Duneyr, and Durathor, from whose horns honey-dew dropped down upon the earth and furnished the water for all the rivers in the world.
In the seething cauldron Hvergelmir, close by the great tree, a horrible dragon, called Nidhug, continually gnawed the roots, and was helped in his work of destruction by countless worms, whose aim it was to kill the tree, knowing that its death would be the signal for the downfall of the gods.
“Through all our life a tempter prowls malignant,
The cruel Nidhug from the world below.
He hates that asa-light whose rays benignant
On th’ hero’s brow and glitt’ring sword bright glow.”
Viking Tales of the North (R. B. Anderson).
Scampering continually up and down the branches and trunk of the tree, the squirrel Ratatosk (branch-borer), the typical busybody and tale-bearer, passed its time repeating to the dragon below the remarks of the eagle above, and vice versa, in the hope of stirring up strife between them. 
The Bridge Bifröst
It was, of course, essential that the tree Yggdrasil should be maintained in a perfectly healthy condition, and this duty was performed by the Norns, or Fates, who daily sprinkled it with the holy waters from the Urdar fountain. This water, as it trickled down to earth through branches and leaves, supplied the bees with honey.
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;
Shines from his sword
The Val-god’s sun. 
The stony hills are dashed together,
The giantesses totter;
Men tread the path of Hel,
And heaven is cloven.”
Sæmund’s Edda (Thorpe’s tr.).
Now although the original inhabitants of heaven were the Æsir, they were not the sole divinities of the Northern races, who also recognised the power of the sea- and wind-gods, the Vanas, dwelling in Vana-heim and ruling their realms as they pleased. In early times, before the golden palaces in Asgard were built, a dispute arose between the Æsir and Vanas, and they resorted to arms, using rocks, mountains, and icebergs as missiles in the fray. But discovering ere long that in unity alone lay strength, they composed their differences and made peace, and to ratify the treaty they exchanged hostages.