Magic, both benevolent (white) and malign (black), has been practiced in the British Isles since at least the Iron Age (800 BCE-CE 43). "Curse tablets"--metal plates inscribed with curses intended to harm specific people--date from the Roman Empire. The Anglo-Saxons who settled in England in the fifth and sixth centuries used ritual curses in documents, and wrote spells and charms. When they became Christians in the seventh century, the...