In Dialogue on Miracles, the thirteenth-century preacher and historian Caesarius of Heisterbach tells of a man curious to discover the origin of the migratory swallows that appeared at his house every spring. Catching one of them, he attached a note to its leg that read, “O swallow, where do you live in winter?” The following spring, a bird appeared with a reply attached to its leg: “In Asia, at Peter’s house.”