The Extant Works of the Writers of that Age
1 There flourished many learned men in the Church at that time, whose letters to each other have been preserved and are easily accessible. They have been kept until our time in the library at Ælia, which was established by Alexander, who at that time presided over that church. We have been able to gather from that library material for our present work.
2. Among these Beryllus has left us, besides letters and treatises, various elegant works. He was bishop of Bostra in Arabia. Likewise also Hippolytus, who presided over another church, has left writings.
3. There has reached us also a dialogue of Caius, a very learned man, which was held at Rome under Zephyrinus, with Proclus, who contended for the Phrygian heresy. In this he curbs the rashness and boldness of his opponents in setting forth new Scriptures. He mentions only thirteen epistles of the holy apostle, not counting that to the Hebrews with the others. And unto our day there are some among the Romans who do not consider this a work of the apostle.
Source: Church History (New Advent)