St. Augustine, also known as Aurelius Augustinus, was one of the key figures in the transition from classical antiquity to the Middle Ages. He was born at Thagaste, in north Africa, and died as the invading Vandals were closing in on his episcopal city, Hippo. He lived through nearly eighty years of the social transformation, political upheavals, and military disasters that are often referred to as the "decline of the Roman Empire." His life also spanned one of the most important phases in the transition from Roman paganism to Christianity. The old Roman pagan tradition was by no means dead, although the Roman emperors had been Christians since Constantine's conversion some forty years before Augustine was born. Augustine's youth saw the brief rule of Julian the Apostate as well as the last great pagan reaction in the empire, which broke out in the 390s...