The first of the authors considered to be Church Fathers are called the Apostolic Fathers. While also dealing with doctrinal issues, these authors are more generally seen as guiding the way of life of those who walk in the footsteps of Christ and his apostles. Clement of Rome, whose Letter to the Corinthians was written c. 96, was a successor to the apostle Peter as the bishop of Rome. His strong appeal to the Church at Corinth to cease its conflicts and disagreements is made with a sense of authority and duty. This letter was well received and respected, reestablished unity within the Church of Corinth, and has been judged by some as confirming the primacy of the bishop of Rome. Ignatius of Antioch, who suffered martyrdom under the emperor Trajan around 110, is renowned for seven letters he wrote to different Christian communities. He bears witness to a hierarchical structure of bishops, priests, and deacons in the early church. His strongest attacks against heresy were aimed at the Docetists, as he affirms the divinity and true humanity of Christ. The Didache, perhaps written in the 80s and 90s, may be the earliest Patristic document. It sets out in clear terms the difference between the demands of a Christian life and the evils of paganism. It is also considered the first code of canon law directing the lives of those in primitive Christian communities. Polycarp, the author of a Letter to the Philippians and a bishop of Smyrna, was a disciple of John the Evangelist. He also wrote a strong recommendation for the letters of Clement, many of which do not survive, and taught St. Irenaeus before suffering martyrdom c. 155 CE. In his surviving letter, written to the Philippians, he fought against the errors of Docetism and the demands of the Judaizers, who required converts to become Jews in order to become Christians. He urged a way of life that stressed charity, almsgiving, and prayer, including prayer for civil authorities. Another disciple of John and a friend of Polycarp was Papias. Only fragments of his work exist, but the surviving material is important, since it is the earliest witness to the authorship of the Gospels. Another work that is generally listed among the writings belonging to the era of those who may have had contact with the Apostles is The Shepherd of Hermas. This treatise was respected for its many moral exhortations and was even considered canonical by some in the early Christian era. Its theme of the two cities is noted as a possible source for St. Augustine’s portrait of the two cities in The City of God.