Russell points out that Augustine's views are limited to time and place and his own community, but later, others took what he said and applied it outside those parameters in ways Augustine never imagined or intended. Works Augustine was one of the most prolific Latin authors in terms of surviving works, and the list of his works consists of more than one hundred separate titles. They include apologetic works against the heresies of the Arians, Donatists, Manichaeans and Pelagians; texts on Christian doctrine, notably De Doctrina Christiana (On Christian Doctrine); exegetical works such as commentaries on Genesis, the Psalms and Paul's Letter to the Romans; many sermons and letters; and the Retractationes, a review of his earlier works which he wrote near the end of his life. Apart from those, Augustine is probably best known for his Confessions, which is a personal account of his earlier life, and for De civitate Dei (The City of God, consisting of 22 books), which he wrote to restore the confidence of his fellow Christians, which was badly shaken by the sack of Rome by the Visigoths in 410. His On the Trinity, in which he developed what has become known as the 'psychological analogy' of the Trinity, is also considered to be among his masterpieces, and arguably of more doctrinal importance than the Confessions or the City of God. He also wrote On Free Choice of the Will (De libero arbitrio), addressing why God gives humans free will that can be used for evil. Legacy In both his philosophical and theological reasoning, Augustine was greatly influenced by Stoicism, Platonism and Neoplatonism, particularly by the work of Plotinus, author of the Enneads, probably through the mediation of Porphyry and Victorinus (as Pierre Hadot has argued). Some Neoplatonic concepts are still visible in Augustine's early writings. His early and influential writing on the human will, a central topic in ethics, would become a focus for later philosophers such as Schopenhauer, Kierkegaard, and Nietzsche. He was also influenced by the works of Virgil (known for his teaching on language), and Cicero (known for his teaching on argument). In philosophy Philosopher Bertrand Russell was impressed by Augustine's meditation on the nature of time in the Confessions, comparing it favourably to Kant's version of the view that time is subjective. Catholic theologians generally subscribe to Augustine's belief that God exists outside of time in the "eternal present"; that