KEYS. Doors held shut with bars, and bars and bolts, were common long before locks and keys became prevalent. Some of the oldest myths reflect this. In Babylonian mythology, for example, Marduk makes gates to the heavens and secures them with bolts. Many later divinities in the ancient world were both guardians of closed doors and bearers of keys.

The possession of keys usually signified power over regions guarded by the locks that the keys could open or close. The regions in question were often the underworld or places of the afterlife—for example, the realm of Hades, the Abyss in the Book of Revelation, and the Mandaean "dark worlds" that had locks and keys different from all others. The keeper of keys was charged not only with guarding the passage as human beings went from this world to the next but also with keeping the dead where...