The City of God, is a book of Christian philosophy written in Latin by Augustine of Hippo in the early 5th century AD. The book was in response to allegations that Christianity brought about the decline of Rome and is considered one of Augustine's most important works.The City of God is a cornerstone of Western thought, expounding on many profound questions of theology, such as the suffering of the righteous, the existence of evil, the conflict between free will and divine omniscience, and the doctrine of original sin.Augustine is recognized as a saint in the Catholic Church, the Eastern Christian Church, and the Anglican Communion and as a preeminent Doctor of the Church. Many Protestants, especially Calvinists and Lutherans, consider him to be one of the theological fathers of the Protestant Reformation due to his teachings on salvation and divine grace. Lutherans, and Martin Luther in particular, have held Augustine in preeminence (after the Bible and St. Paul). Luther himself was a member of the Order of the Augustinian Eremites (1505–1521).