The encounter with Islam impacted Christianity in many ways, and was one of the contributing factors in one of the most acrimonious debates in the Eastern church—the iconoclast controversy. The question was whether the use of icons (pictures of Jesus, Mary, and the saints) violated the biblical commandment prohibiting the worship of graven images. ‘Byzantines and Franks’ discusses the battle between the iconoclasts and the iconodules, and how, despite these troubles, Christianity continued to grow in the East and West. However, by the eleventh century, the “Great Schism” that divided the Christian world into the Orthodox East and the Catholic West had begun. The Crusades and the sack of Constantinople in 1204 deepened the divide.