The insertion in such a work as this of what seems almost technical in its character has this twofold purpose: first, to give a glimpse of the grounds of our knowledge of Constantine, with a view of how far and in what directions it has been worked out through literature; second, to serve the expressed purpose of this series, of encouraging farther study in its lines. The very knowledge of what the sources are, and their character, apart from any special study of them, gives a width of horizon and definiteness of conception to the general student, which can hardly be gotten in any other way; while for any one who plans farther study in any line, it is of first importance to find the what and where of his material.