Pecci taught Thomism, the theology and philosophy of St Thomas Aquinas, at the Pontifical Gregorian University in Rome in 1847. At the request of his brother, who became Archbishop of Perugia, he was made a professor at the theological seminary in Perugia, where he remained, from 1852 through 1859. After the city was taken over by Piedmont forces in 1860, Pope Pius IX called him to Rome and offered him a professorship in theology at La Sapienza University. Pope Pius also called him into the papal commission to prepare the First Vatican Council. Good Thomist theology was hard to come by at that time, with the result that young scholars from other countries were sent to Rome to learn from Pecci and Tommaso Maria Zigliara. In 1870 he resigned his professsorship because he refused to take the