The depiction of Muslims as pagans and idolaters ultimately gave way after the First Crusade to the belief that Islam was a form of Christian heresy. This perception, prominent by the twelfth century, actually found expression already in the first century of Christianity's encounter with Islam in the writings of John of Damascus. John was an eighth-century theologian from Syria who spent part of his career serving in the government of Caliph Abd al-Malik in Damascus before resigning his post and joining the St. Sabbas Monastery near Jerusalem. He is best known for his defense of the use of icons and images in Christian worship over against those who wanted to destroy images out of fear that Christians were worshipping them. The prominent place that the veneration of icons has held historically in Eastern Orthodox Christianity since the eighth century is due in part to John's theological defense of them.

XREF: Connects to the broader history of Christian-Muslim polemics and Byzantine theological debates. Builds on: "Crusaders reframed Islam as paganism to justify conquest"

Green, Todd H, The Fear of Islam_ An Intro…, loc. 128