Augustine (A.D. 354-430) was born in northern Africa (roughly modern Algeria). Monica, his devout Christian mother, raised him in biblical truth, prayed for him faithfully throughout her life, and remained an important influence on Augustine until her death. His brilliant but restless mind, however, wandered away from his Christian roots. This journey away from God (detailed in his classic Confessions) included giving himself to sensual pleasures. Augustine, seeking intellectual and spiritual fulfillment, wandered in succession through pagan philosophies such as Manichaeanism and Neoplatonism. Manichaeanism combined elements from several religions, teaching that reality is ultimately grounded in two gods, one evil and one good. Neoplatonism, however, taught that all reality emanated from "the One" (an impersonal, unknowable god).
Augustine eventually realized the intellectual and spiritual failure of his search through paganism. After his soul came to rest through conversion to Christ, Augustine would become the greatest theologian and apologist of the first Christian millennium. He powerfully refuted prevailing pagan philosophies (including Manichaeanism) as well as heresies that threatened to divide and corrupt the church. In The City of God, Augustine brilliantly confronted the pagan charge that Christianity was responsible for the downfall of the Roman Empire. He focused the blame, where it belonged by exposing paganism's spiritual bankruptcy. Moreover, in so doing, Augustine constructed a grand philosophy of history in observing that the crisis of his day was only part of a larger whole. The "City of the World," comprised of those chief love is the self, stands in sharp contrast in every age to the “City of God,” of those who love God.
Extracted from the Apologetics Study Bible.