“Guglielmo Marconi, the inv­e­n­tor of the radio, believed that sound waves never completely die away, that they persist...masked by the day-to-day noise of the world. Marconi thought that if he could only invent a microphone powerful enough, he would be able to listen to the sound of ancient times. The Sermon on the Mount, the footfalls of Roman soldiers marching down the Appian Way.”