The work Aquinas did in the next sixteen years changed the face of Western Christianity and philosophy. He wrote commentaries on virtually everything Aristotle wrote; he wrote on the Book of Job, the Gospel of John, and Paul’s epistles; he wrote a seminal treatise on the nature of evil and another on building aqueducts and on military siege operations.21 Above all, he also wrote the two works that would earn him the title of Universal Doctor of the Catholic Church: the Summa Contra Gentiles and Summa Theologica.
