The City of God by Augustine

Augustine's earlier work, the Confessions, is his most popular and well-known work. After Augustine's death in 430, his theological innovations began their 1,100-year hegemony over European ideology up until the Protestant Reformation started in 1517. The city of God is a book in which we learn about original sin, innate depravity, the actual mechanics of hell and heaven. It's a long book; an audio summary of it will take a little while.