It is perhaps generally assumed that the men of the middle ages were widely read in and deeply influenced by the fathers of the early church, but at least for our subject this influence has hardly been treated either broadly or in detail. Indeed, the predilection of the humanists of the fifteenth and sixteenth centuries for anything written in Greek and their aversion to medieval Latin has too long operated as a bar to the study of medieval literature in general. And scholars who have edited or studied the Greek, Syriac, and other ancient texts connected with early Christianity have perhaps too often neglected the Latin versions preserved in medieval manuscripts, or, while treasuring up every hint that Photius lets fall, have failed to note the citations and allusions in medieval Latin encyclopedists. Yet it is often the case that the manuscripts containing the Latin versions are of earlier date than those which seem to preserve the Greek original text. [Sidenote: Method of presenting early Christian thought.] There is so much repetition and resemblance between the numerous Christian writers in Greek and Latin of the Roman Empire that I have even less than in the case of their classical contemporaries attempted a complete presentation of them, but, while not intending to omit any account of the first importance in the history of magic or experimental science, have aimed to make a selection of representative persons and typical passages. At the same time, in the case of those authors and works which are discussed, the aim is to present their thought in sufficiently specific detail to enable the reader to estimate for himself their scientific or superstitious character and their relations to classical thought on the one hand and medieval thought on the other.