Walter Richard Cassels, The Gospel According to Peter: A Study
“ Some critics, impressed apparently with the idea that no early Gospels can possibly be otherwise than dependent on our canonical works, yet having to explain the continuous divergence from the canonical narratives, advance the suggestion, that the writer of the Gospel according to Peter may have derived all the points which the fragment contains, in common with one or more of the canonical Gospels, from a Harmony of our Gospels. Now, the only Harmony of the second century which, they think, has survived is the so-called “Diatessaron” of Tatian. ”
