Development of the New Testament canon a novelty in Irenaeus's time. "Against Heresies" 3.11.7 acknowledges that many heterodox Christians use only one gospel while 3.11.9 acknowledges that some use more than four. The success of Tatian's Diatessaron in about the same time period is "...a powerful indication that the fourfold Gospel contemporaneously sponsored by Irenaeus was not broadly, let alone universally, recognized." Irenaeus apparently quotes from 21 of the New Testament books and names the author he thought wrote the text. He mentions the four gospels, Acts, the Pauline epistles with the exception of Hebrews and Philemon, as well as the first epistle of Peter, and
Development of the New Testament canon as now known): In the mid-2nd century, Justin Martyr (whose writings span the period from c. 145 to 163) mentions the "memoirs of the apostles", which Christians called "gospels" and which were regarded as on par with the Old Testament. Scholars are divided on whether there is any evidence that Justin included the Gospel of John among the "memoirs of the apostles", or whether, on the contrary, he based his doctrine of the Logos on it. Justin quotes the letters of Paul, 1 Peter, and Acts in his writings. In Justin's works, distinct references are found to Romans, 1 Corinthians,