According to the Scrolls of Elsene, in the days when the High People ruled, their Iphendi would seize human children from Midworld to serve as Caretakers in their magic gardens on Muraius.
These children would be raised in hermetic isolation from humankind, forbidden to form attachments to others so that they may be taught Yevna's divine truths, such as the locations of the ley lines in the world below, and the secret of the God Tree's power. The Caretakers were gifted supernaturally long life in exchange for their service.