In this short article I would like to draw attention to a published but neglected Syriac text that provides unambiguous evidence of the existence of a Christian baptismal rite in the twelfth-century Jazirah (upper Mesopotamia), put under the patronage of John the Baptist, which allowed for the baptism of Muslim children as a means of affording them spiritual protection, but without effecting their conversion to Christianity. The very idea of such a rite may sound strange to modern ears, especially to those of us who live outside the Middle East, and who have mostly come to regard Christianity and Islam as quite distinct , and often hostile, entities, with little overlap of belief and worship. For many centuries after the Arab conquest of Syria and Iraq, however, there was continuous interaction between the two communities at every social level. Many families included converts to the new religion, villages and towns contained adherents to both faiths, and there was frequent intermarriage. While some scholarly converts to Islam received a thoroughgoing Islamic education and used their knowledge of the texts and doctrines of their former religion to compose refutations of it, numerous other converts continued to live much as before and carried many of their old beliefs and practices with them. So whilst Muslim and Christian theologians debated t he philosophical and theological niceties of their faith, and expounded orthodox religious practice, a large proportion of their followers were far more concerned with older religious priorities, such as the health and prosperity of family, livestock, and crops, and warding themselves against the unwanted attention of evil powers, whether demons, jinns, or the evil eye. Many Muslims continued to use the sign of the cross on bread and buildings, or even as a tattoo on women's foreheads, as a means of protection, and as early as the eleventh century, as attested by the Church of the East writer Elijah of Nisibis (975-1046), some Christian men of his community had adopted the Muslim practice of circumcision, although he put it rather differently: ‘We follow the custom of our Lord and of his holy disciples in practising circumcision'. Popular religion was no respecter of theological doctrine and law, Muslim or Christian.