It is hard to overestimate the importance of Augustine's work and influence, both in his own period and in the history of Western philosophy after it. Patristic philosophy and theology, and every area of philosophy and theology in the later medieval period, manifest the mark of his thought. In fact, at least until the thirteenth century, when he may have had a competitor in Thomas Aquinas, Augustine is undoubtedly the most important philosopher of the medieval period. Furthermore, although his influence is somewhat less after the medieval period, it is still important. Many of his views, including, for example, his theory of the just war, his account of time and eternity, his understanding of the will, his attempted resolution of the problem of evil, and his approach to the relation of faith and reason, have continued to be important up to the present.