The Epistle of Polycarp to the Philippians

Of Polycarp's life little is known, but that little is highly
interesting. Irenaeus was his disciple, and tells us that "Polycarp was
instructed by the apostles, and was brought into contact with many who
had seen Christ" (Adv. Haer., iii. 3; Euseb. Hist. Eccl., iv. 14).