The first Christians to encounter Islam were not Latin-speakers from the western Mediterranean or Greek-speakers from Constantinople but Mesopotamian Christians who spoke the Aramaic dialect of Syriac. Under Muslim rule from the seventh century onward, Syriac Christians wrote the most extensive descriptions extant of early Islam. Seldom translated and often omitted from modern historical reconstructions, this vast body of texts reveals a complicated and evolving range of religious and cultural exchanges that took place from the seventh to the ninth century. The first book-length analysis...