Confessions of St. Augustine

Confessions (Latin: Confessiones) is an autobiographical work by Augustine of Hippo, consisting of 13 books written in Latin between AD 397 and 400. The work outlines Augustine's sinful youth and his conversion to Christianity. Modern English translations are sometimes published under the title The Confessions of Saint Augustine in order to distinguish it from other books with similar titles. Its original title was Confessions in Thirteen Books; it was composed to be read out loud, with each book being a complete unit.
Confessions is generally considered one of Augustine's most important texts. It is widely seen as the first autobiography written in the Western world (Ovid had invented the genre at the start of the first century AD with his Tristia) and was an influential model for Christian writers throughout the Middle Ages. Henry Chadwick wrote that Confessions will "always rank among the great masterpieces of western literature".

(This summary is from Wikipedia.)