What evidence is there that Peter was a bishop in Rome?

The Encyclopaedia Brittanica says > The claims that the church of Rome was founded by Peter or that he served as its first bishop are in dispute and rest on evidence that is not earlier than the middle or late 2nd century. Where in the Bible does it say that Peter was a Bishop? Also, are there any non-biblical 1st-century historical accounts that mention his being the Bishop of Rome?