Church History by Eusebius Pamphilius
Chapter XV.--Clement, the Third Bishop of Rome.
In the twelfth year of the same reign Clement succeeded Anencletus after the latter had been bishop of the church of Rome for twelve years. The apostle in his Epistle to the Philippians informs us that this Clement was his fellow-worker. His words are as follows: |With Clement and the rest of my fellow-laborers whose names are in the book of life.|