Como, Italy—In the façade of the Cathedral of Santa Maria Assunta, better known as the Como Cathedral, are statues depicting various saints, the Virgin Mary, and the Archangel Gabriel. Also displayed among them, though, is the figure of a Roman official famous for his role in establishing the empire’s policy of persecution against the Christian church. Not long after being appointed governor over the province of Bithynia-Pontus, in modern-day Turkey, Pliny the Younger wrote to the Emperor Trajan about the growing problem of a new religious sect known as Christians. He put a series of questions to Trajan about their...