The just war theory by Thomas Aquinas has had a lasting impact on later generations of thinkers and was part of an emerging consensus in Medieval Europe on just war. In the 13th century Aquinas reflected in detail on peace and war. Aquinas was a Dominican friar and contemplated the teachings of the Bible on peace and war in combination with ideas from Aristotle, Plato, Saint Augustine and other philosophers whose writings are part of the Western canon. Aquinas' views on war drew heavily on the "Decretum Gratiani", a book the Italian monk Gratian had compiled with passages from the Bible. After its publication in the 12th century, the "Decretum Gratiani" had been republished with commentary from Pope Innocent IV and the Dominican friar Raymond of Penafort. Other significant influences on Aquinas just war theory were Alexander of Hales and Henry of Segusio.