At this date we have attention called to the discrepancy between the Gospels as to the date of the Crucifixion by Claudius Apollinaris.

We have also Tatian, the Epistle of the Churches of Vienne and Lyons, the heathen Celsus and the Muratorian Canon, and then a very few years later Theophilus of Antioch and Irenaeus.
I imagine that there can be really no doubt about Tatian.

Whatever may have been the nature of the Diatessaron, the 'Address to the Greeks' contains references which it is mere paradox to dispute.

I will not press the first of these which is given by Dr.Westcott, not because I do not believe that it is ultimately based upon the fourth Gospel, still less that there is the slightest contradiction to St.John's doctrine, but because Tatian's is a philosophical comment perhaps a degree too far removed from the original to be quite producible as evidence.

It is one of the earliest speculations as to the ontological relation between the Father and the Son.