Pope Clement I wrote this letter to the Church at Corinth after a leadership dispute broke out there, and the Corinthians appealed to him. (He told them to reaffirm the recently rejected leaders in their former offices.) This may be the first exercise of papal primacy outside the New Testament.
The letter is most often dated to the A.D. 90s, but there are significant reasons to date it earlier. Internal evidence--including a reference to the Jerusalem Temple still functioning (it was destroyed in mid A.D. 70) and a series of repeated calamities in Rome (possibly the "year of four emperors" that took place in A.D. 69)--points to a date in A.D. 69 or 70. Whether an earlier or a later date is preferred, it is an important witness to the role of Rome in the first century.
The author may be the same Clement mentioned by St. Paul in Philippians 4:3. --Jimmy Akin