De doctrina Christiana, On Christian Doctrine, is a famous treatise by Augustine of Hippo, consisting of four books that describe how to interpret and teach the Scriptures. The first three books, published in 397, set three tasks for Christian teachers and preachers: to discover the truth in the contents of the Scriptures, to teach the truth from the Scriptures, and to defend scriptural truth when it was attacked. It is believed that the last part of book three and the totality of book four were added much later, in 426. The fourth book is especially quoted for being the first treatment of the relation between Christianity and Ancient Rhetoric. Summary by Leni.