Tatian's Diatessaron as Evidence for Second-Century Gospel Use

The evidence explained

Tatian, a student of Justin Martyr, produced the Diatessaron ('through the four') by weaving Matthew, Mark, Luke, and John into a single sequential narrative, apparently intending it as a usable gospel text for liturgical or catechetical purposes rather than as a scholarly harmony in the modern sense. No complete copy of the original Syriac or Greek text survives; scholars reconstruct its content from later translations, quotations in Ephrem the Syrian's commentary, and fragments such as a small Greek fragment discovered at Dura-Europos, generally dated to before the mid-third century, which confirms the work's early circulation.

The significance of the Diatessaron lies in what it presupposes: that by roughly AD 170, in a Christian community with connections stretching from Rome to Syria, four specific gospels, and no others, were considered the primary or exclusive sources worth harmonizing. This is treated by scholars including Bruce Metzger as important evidence for the developing fourfold gospel canon predating formal conciliar decisions by more than a century, corroborating similar implications from Irenaeus's near-contemporary insistence, around AD 180, that there must be exactly four gospels.

Scholars debate the extent to which Tatian incorporated material from extracanonical sources; some patristic evidence and later Diatessaronic witnesses contain minor material not clearly traceable to the four canonical gospels, leading scholars such as William Petersen to argue for some non-canonical infiltration, though this remains a minority reading contested by others including Metzger, who maintain the work is overwhelmingly, if not exclusively, based on the four gospels.

The Diatessaron's later history, particularly its eventual suppression in Syriac-speaking churches in favor of the separated gospels, likely by the fifth century under bishops such as Rabbula of Edessa, is itself indirect evidence that ecclesiastical authorities came to prefer the four discrete texts over a harmonized version, reinforcing rather than undermining the fourfold gospel's entrenched status by that period.