Actually, it began shortly after Pentecost, when Matthias was chosen to replace Judas. Although the terms “bishop,” “priest,” and “deacon” were somewhat fluid in the apostolic age, by the beginning of the second century they had achieved the fixed form in which they are used today to designate the three offices whose functions are clearly distinct in the New Testament.
The early Church Fathers recognized all three offices and regarded them as essential to the Church’s structure. Especially significant are the letters of Ignatius, Bishop of Antioch, who traveled from his home city to Rome, where he was executed around A.D. 110. On the way he wrote letters to the churches he passed. Each of these churches possessed the same threefold ministry. Without this threefold ministry, Ignatius said, a group cannot be called a church.
Or how 'bout the writings of St. John Chrysostom:"[In Philippians 1:1 Paul says,] ‘To the co-bishops and deacons.’ What does this mean? Were there plural bishops of some city? Certainly not! It is the presbyters that [Paul] calls by this title; for these titles were then interchangeable, and the bishop is even called a deacon. That is why, when writing to Timothy, he says, ‘Fulfill your diaconate’ [2 Tim. 4:5], although Timothy was then a bishop. That he was in fact a bishop is clear when Paul says to him, ‘Lay hands on no man lightly’ [1 Tim. 5:22], and again, ‘Which was given you with the laying on of hands of the presbytery’ [1 Tim. 4:14], and presbyters would not have ordained a bishop" (Homilies on Philippians 1:1 [A.D. 402]).
In fact, when Paul told Timothy, “[W]hat you have heard from me before many witnesses entrust to faithful men who will be able to teach others also” (2 Tim. 2:2) he was referring to the first four generations of apostolic succession—his own generation, Timothy’s generation, the generation Timothy will teach, and the generation they in turn will teach.