The Seven Keys were created by a concerted effort by the gods of Good and the god of Nature to repair the damage done by the Dark One, the most powerful of the gods of evil. He created seven links between his seven realms and Aerth, through which he planned to slowly leak evil into the world and eventally form portals through which his minions, and eventually he himself, could pass through. The work on the Keys was finished, and the Keys hidden, before the world of Aerth was declared complete. Now it is up to the people of Aerth to decide their eventual fate, either a world in Balance as was the gods' original agreement, or another realm of Evil.
The keys are shaped like small stars, about the size of a child's hand. They appear to be made of delicate crystal, but they are unbreakable. When sent through a portal created by one of the Dark One's links, it will close the portal and destroy the link forever.