allinye:

The Norns are beings who rule the destinies of gods and mortals. The most important of these women are three sisters known as Urðr (fate), Verðandi (necessity) and Skuld (being). They live beneath the world tree Yggdrasil, by the well called Urðarbrunnr. The Norns are responsible for keeping the tree healthy by pouring mud and water from the well over its roots.