Polycarp was a correspondent of Ignatius of Antioch. Ignatius addressed a letter to him, and mentions him in the letters to the Ephesians and to the Magnesians. Polycarp visited Rome during the time of Pope Anicetus, and found their customs for observing Easter differed. They agreed to peaceably disagree on this matter.
His sole surviving work, the Letter to the Philippians, and an account of The Martyrdom of Polycarp form part of the collected writings of the Ante-Nicene Fathers.
Irenaeus relates how and when he became a Christian and in his letter to Florinus stated that he saw and heard him personally in lower Asia; in particular he heard the account of Polycarp's intercourse with John the Evangelist and with others who had seen Jesus Christ. Irenaeus also reports that Polycarp was converted to Christianity by apostles, was consecrated a bishop, and communicated with many who had seen Jesus. He repeatedly emphasizes the very old age of Polycarp.
The date of Polycarp's death is disputed. Eusebius dates it to the reign of Marcus Aurelius, circa 167-8. However, a post-Eusebian addition to the treatise The Martyrdom of Polycarp dates his death to Sunday, February 23 in the proconsulship of Statius Quadratus -- which works out to be 155 or 156. This earlier date better fits the tradition of his association with Ignatius and John the Evangelist.