The Epistles of Clement, Matheses, Polycarp, and Ignatius are included among the Apostolic Fathers. The authors were personally acquainted with the Apostles. Clement, Bishop of Rome was a disciple of Saint Peter. Ignatius was the second successor of St. Peter in the See of Antioch. An accepted tradition declares him a disciple of St. John. Polycarp was "instructed by Apostles", according to Irenaeus and had been a disciple of St. John nearly twenty years. These Epistles were written in the late first and early second century and provide great insight into early Christian thought.