Long before religions based on a belief in one god, such as Judaism, Christianity, and Islam, became the dominant religions of the world, most cultures believed in more than one god, or were polytheistic. At the center of this ancient belief system was the idea that the world is controlled by powers that are both visible and invisible, and people relied on magic—the use of means believed to have supernatural power over natural forces—to understand and control their environment. Archaeologists, scientists who study the remains of ancient cultures, and scholars have discovered cave drawings dating back as far as 17,000 years that depict the practice of magic. In an ancient community one or two people possessed the wisdom and skill to work magic, which involved making potions and casting spells to bring about certain effects or events. They predicted the future, gave advice...