In part 1, I quoted a passage from Jerome in which he states that presbyters and bishops were the same, and that a time came when it was universally decreed in the church that one presbyter should preside over the others, in order to remove the seeds of schism.
What was this “universal decree” that he alludes to?
The Universal Decree
It was suggested in Part 2 that this decree only required that bishops be ordained from among the presbyters, and that it did not necessarily originate the separate office of bishop, which was present in apostolic times.
The time and place of this decree is not given, though Jerome seems to assume that his readers have knowledge of it. The mention of “the church” making the decision might suggest that this occurred in post-apostolic times, though it is not conclusive.
Hegesippus’s Second Council of Jerusalem
I can only think of one potential event that Jerome might have been referring to: the gathering of the surviving apostles and disciples of the Lord to Jerusalem shortly after the destruction of the city in AD 70. This is mentioned by Hegesippus (d. c. 185), who states that it was for the purpose of choosing a successor to James:
After the martyrdom of James and the conquest of Jerusalem which immediately followed, it is said that those of the apostles and disciples of the Lord that were still living came together from all directions with those that were related to the Lord according to the flesh (for the majority of them also were still alive) to take counsel as to who was worthy to succeed James. They all with one consent pronounced Symeon, the son of Clopas, of whom the Gospel also makes mention; to be worthy of the episcopal throne of that parish. He was a cousin, as they say, of the Saviour. For Hegesippus records that Clopas was a brother of Joseph.apud Eusbeius, Hist. eccl. 3.11.1-2.
Jerome is known to have been familiar with Hegesippus’s now-lost Memoirs.
The Situation Following AD 70
The period following the Neronian persecutions and the destruction of Jerusalem was certainly a transitional one. It had been over forty years after the ministry of Jesus, and by then most of the apostles and those they had ordained as successors were dead. Indeed, according to Clement of Alexandria and Chrysostom, all of the twelve apostles had died by the time of the destruction of Jerusalem. The reference to “apostles” in Hegesippus may refer to other surviving eyewitness disciples, and perhaps to the seventy(-two) disciples who were thought to have been sent out by Christ.
There would likely have been a need for a new generation of bishops to be ordained in the churches which had been orphaned by the deaths of the apostles, and perhaps general instructions or guidelines were given at this council in Jerusalem for ordaining these bishops from the established presbytery of those churches.
As I have argued elsewhere, a comparative study of Clement Alex. and the Acts of John suggests that it was from this time that John the Evangelist began ordaining bishops in the churches of Asia.
This is merely a suggestion, but alternative explanations seem lacking.