At this time (= the time of Clement of Alexandria, early third century CE) Rhodo, a native of Asia, who had been instructed, as he himself states, by Tatian, with whom we have already become acquainted, having written several books, published among the rest one against the heresy of Marcion. (Church History 5.13.1)
The fact that Rhodo or Corodo was part of the Diatessaron tradition is interesting as it helps provide a context for the debate between him and the Marcionites. Eusebius goes on to say that Rhodo or Corodo testifies that:
this heresy (= Marcionitism) was divided in his time into various opinions; and while describing those who occasioned the division, he refutes accurately the falsehoods devised by each of them.
And then he quotes Rhodo or Corodo to the effect that:
Therefore also they disagree among themselves, maintaining an inconsistent opinion. For Apelles, one of the herd, priding himself on his manner of life and his age, acknowledges one principle, but says that the prophecies are from an opposing spirit, being led to this view by the responses of a maiden by name Philumene, who was possessed by a demon. But others, among whom are Potitus and Basilicus, hold to two principles, as does the mariner Marcion himself. These following the wolf of Pontus, and, like him, unable to fathom the division of things, became reckless, and without giving any proof asserted two principles. Others, again, drifting into a worse error, consider that there are not only two, but three natures. Of these, Syneros is the leader and chief, as those who defend his teaching say.
The fact that Rhodo only has direct knowledge of the opinions of this Marcionite (= Apelles) but cites the opinions of 'dualist' Marcionites from hearsay is important to note. Rhodo or Corodo goes on to tell us from direct correspondence with Apelles the following:
For the old man Apelles, when conversing with us, was refuted in many things which he spoke falsely; whence also he said that it was not at all necessary to examine one's doctrine, but that each one should continue to hold what he believed. For he asserted that those who trusted in the Crucified would be saved, if only they were found doing good works. But as we have said before, his opinion concerning God was the most obscure of all. For he spoke of one principle, as also our doctrine does. Then, after stating fully his own opinion, he adds: When I said to him, Tell me how you know this or how can you assert that there is one principle, he replied that the prophecies refuted themselves, because they have said nothing true; for they are inconsistent, and false, and self-contradictory. But how there is one principle he said that he did not know, but that he was thus persuaded. As I then adjured him to speak the truth, he swore that he did so when he said that he did not know how there is one unbegotten God, but that he believed it. Thereupon I laughed and reproved him because, though calling himself a teacher, he knew not how to confirm what he taught.
It is curious that Apelles refuses to engage Rhodo directly with scriptural arguments. One would expect that a sophist could come up with any argument possible given what we know of the divergence of opinions in early Christianity all using similar scriptural material.
It is my suspicion that the testimony here is something of an interrogation. The fact that Apelles is already described as an 'old man,' the fact that he refuses to develop heretical arguments (which he certainly could have), the reference to 'swearing' (which echoes the situation in the Letter to Theodore and later Dionysius's letter) and most significantly the fact that Eusebius goes on to say:
In the same work, addressing Callistio (Καλλιστίωνι), the same writer acknowledges that he had been instructed at Rome by Tatian. And he says that a book of Problems had been prepared by Tatian, in which he promised to explain the obscure and hidden parts of the divine Scriptures. Rhodo himself promises to give in a work of his own solutions of Tatian's problems. There is also extant a Commentary of his on the Hexæmeron. But this Apelles wrote many things, in an impious manner, of the law of Moses, blaspheming the divine words in many of his works, being, as it seemed, very zealous for their refutation and overthrow. So much concerning these.
Hilgenfeld rightly notes that 'Callistion' is another example of the -ίων ending being used as a diminutive suffix, 'Marcion' being another. The Roman context of the reference (i.e. stressing his loyalty to Rome, and the Roman background of Tatian his teacher) all confirms that he is writing to Callistus the bishop of Rome opposed by Hippolytus in his letters.
When you put all these pieces together it would seem that we have a situation where Rhodo - himself a 'heretic' insofar as he used a Diatessaron and was allied with Tatian - is in a strange position of differentiating his own tradition from that of Apelles and the Marcionites. Both would have possessed similar gospels but my guess is that the 'Marcionites' were those loyal to 'Marcion' (the diminutive of 'Marcus') the original bishop of Alexandria. Their gospel was only the Alexandrian text of the Diatessaron. The Roman Church emerged in the third century with some sort of 'compromise position' where four gospels were argued to be 'behind the Diatessaron' which varied from locale to locale.
