Augustinianism is the philosophical and theological system of Augustine of Hippo and its subsequent development by other thinkers, notably Boethius, Anselm of Canterbury and Bonaventure. Among Augustine's most important works are The City of God, De doctrina Christiana, and Confessions. Originally, Augustinianism developed in opposition to Pelagianism; it was widespread in medieval western philosophy until the arrival of Thomism and Aristotelianism. Pope Benedict XVI cautioned that all of the Western Church teaching leads to him: