4. The occasion of his writing is related and settled out of Eusebius. Why this Gospel is attributed to Peter, either as dictator or writer, by some of the ancients?
Eusebius, Church History, book II, chapter 15, sets this forth as the occasion of the Gospel written by Saint Mark, that, with the Romans earnestly requesting of him that he leave with them some written record of that doctrine that they heard from Saint Peter, he considered it worthy of gratification, and so wrote the Gospel:and that Saint Peter, when he had learned of it through revelation of the Holy Spirit, delighted with the zeal of those men, confirmed it with his own authority, that thereafter it might be read in the Churches.Whence perhaps it arose that many of the Greeks, even Athanasius in his tractatu de libris scripturæ, and some Easterners, like Eutychius Alexandrinus, and others, attribute the Gospel received there to Peter as dictator or writer.Which, from the testimony of Papias, in Eusebius’ Church History, book III, chapter 39, the most learned Valesius, in his Annotationibus on this place, advises is thus worthy to be received, that, when Mark had heard the preaching of Peter, by the Spirit of God he studiously digested the individual things that were pertaining to Christ.Nevertheless, this narration of Eusebius, as it rests upon some uncertain hypotheses, and since other ancients also relate that the Gospel was written at Alexandria in Egypt, does not deserve complete confidence.
 Eutychius (born 876) was a physician, who became the Patriarch of Alexandria. His Annals begin with the creation of the world and end with the year 900.