The City of God is a book of Christian philosophy written in Latin by Augustine of Hippo in the early 5th Century. The book was in response to allegations that Christianity brought about the decline of Rome, and is considered one of Augustine's most important work. 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 omnipotence, 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 pre-eminent 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 teaching on salvation and divine grace. Lutherans, and Martin Luther in particular, have held Augustine in pre-eminence (after the bible) and St. Paul). Luther himself was a member of the Order of the Augustinian Eremites (1505-1521).