No book except the Bible itself had a greater influence on the Middle Ages than City of God. Since medieval Europe was the cradle of today's Western civilization, this work by consequence is vital for an understanding of our world and how it came into being.
St. Augustine is often regarded as the most influential Christian thinker after St. Paul, and this book is his masterpiece, a vast synthesis of religious and secular knowledge. It began as a reply to the charge that Christian otherworldliness was causing the decline of the Roman Empire. Augustine produced a wealth of evidence to prove that paganism bore within itself the seeds of its own destruction. Then he proceeded to his larger theme, a cosmic interpretation of history in terms of the struggle between good and evil: the City of God in conflict with the Earthly City or the City of the Devil. This, the first serious attempt at a philosophy of history, was to have incalculable influence in forming the Western mind on the relations of church and state, and on the Christian's place in the temporal order.