In the fourth century, the deserts of Egypt became the nerve center of a radical new movement, what we now call monasticism. Groups of Christians-from illiterate peasants to learned intellectuals-moved out to the wastelands beyond the Nile Valley and, in the famous words of Saint Athanasius, made the desert a city. In so doing, they captured the imagination of the ancient world. They forged techniques of prayer and asceticism, of discipleship and...